Global jackson ObjectMapper not registering custom serializer

I am using Java 17, spring-boot 2.6.3 with spring-webflux and spring-consul dependencies and I have the following class:

import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ClassPathBeanDefinitionScanner;
import org.springframework.context.annotation.Primary;
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
import org.springframework.web.reactive.config.EnableWebFlux;

import com.enterprise.project.model.serializer.ModelSerializer;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.databind.ObjectMapper;

@SpringBootApplication
@EnableWebFlux
public class Application {

    public static void main(final String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    static BeanFactoryPostProcessor beanFactoryPostProcessor(final ApplicationContext beanRegistry) {
        return (final var beanFactory) -> {
            final var beanDefinitionScanner = new ClassPathBeanDefinitionScanner(
                    (BeanDefinitionRegistry) ((AnnotationConfigReactiveWebServerApplicationContext) beanRegistry)
                            .getBeanFactory());
            beanDefinitionScanner.addIncludeFilter(
                    (final var mr, final var mrf) -> !mr.getClassMetadata().getClassName().contains("model"));

            beanDefinitionScanner.scan("com.enterprise.project", "com.enterprise.project.model.serializer");
        };
    }

    @Bean
    @Primary
    public ObjectMapper customObjectMapper(final Jackson2ObjectMapperBuilder builder) {
        return builder.serializationInclusion(JsonInclude.Include.NON_NULL).serializers(new ModelSerializer()).build();
    }
}

Here's my custom serializer.

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.Base64;

import com.enterprise.project.model.FirstModel;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;

public class ModelSerializer extends StdSerializer<FirstModel> {

    private static final long serialVersionUID = -5754330070183741830L;

    public ModelSerializer() {
        this(FirstModel.class);
    }

    public ModelSerializer(final Class<FirstModel> responseModel) {
        super(responseModel);
    }

    @Override
    public void serialize(final FirstModel Model, final JsonGenerator jgen,
            @SuppressWarnings("unused") final SerializerProvider provider) throws IOException {
        jgen.writeStartObject();
        jgen.writeNumberField("one", Model.second());

        final var totalValue = Model.third();
        if (totalValue != null) {
            jgen.writeNumberField("two", totalValue);
        }

        jgen.writeNumberField("three", Model.first().intValue());
        jgen.writeStringField("four", Model.fourth());

        final var surcharge = Model.fifth();
        if (surcharge != null) {
            jgen.writeBooleanField("five", surcharge.booleanValue());
        }

        jgen.writeStringField("six", ModelSerializer.encodeBase64(ModelSerializer.toXML(Model.sixth())));
        jgen.writeEndObject();
    }

    public static String encodeBase64(final String toEncode) {
        return Base64.getEncoder().encodeToString(toEncode.getBytes(StandardCharsets.UTF_8));
    }

    public static <T> String toXML(final T data) {
        try {
            return XmlMapper.builder().build().writeValueAsString(data);
        } catch (@SuppressWarnings("unused") final JsonProcessingException e) {
            return "";
        }
    }
}

And my models are as simples as this:

import java.math.BigDecimal;

import com.fasterxml.jackson.annotation.JsonInclude;

@JsonInclude(JsonInclude.Include.NON_NULL)
public record FirstModel(Integer first, BigDecimal second, BigDecimal third, String fourth, Boolean fifth,
        SecondModel sixth) {
    // In most cases record classes does not need any implementation.
}

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlRootElement;

@JacksonXmlRootElement(localName = "second")
@JsonInclude(JsonInclude.Include.NON_NULL)
public record SecondModel(@JacksonXmlProperty(isAttribute = true) String first,
        @JacksonXmlProperty(isAttribute = true) String second, @JacksonXmlProperty(isAttribute = true) String third,
        @JacksonXmlProperty(isAttribute = true) String fourth, @JacksonXmlProperty(isAttribute = true) String fifth,
        @JacksonXmlProperty(isAttribute = true) String sixth, @JacksonXmlProperty(isAttribute = true) String seventh,
        @JacksonXmlProperty(isAttribute = true) String eighth, @JacksonXmlProperty(isAttribute = true) String ninth,
        @JacksonXmlProperty(isAttribute = true) String tenth, @JacksonXmlProperty(isAttribute = true) String eleventh,
        @JacksonXmlProperty(isAttribute = true) ThirdModel twelfth) {
    // In most cases record classes does not need any implementation.
}

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlRootElement;

@JacksonXmlRootElement(localName = "third")
@JsonInclude(JsonInclude.Include.NON_NULL)
public record ThirdModel(@JacksonXmlProperty(isAttribute = true) String first,
        @JacksonXmlProperty(isAttribute = true) String second, @JacksonXmlProperty(isAttribute = true) String third,
        @JacksonXmlProperty(isAttribute = true) String fourth, @JacksonXmlProperty(isAttribute = true) String fifth) {
    // In most cases record classes does not need any implementation.
}

I can't annotate my model class with @JsonSerialize(using = ModelSerializer.class) because it is in a dependency that I am not allowed to modify. I know I did wrote the code models here, but I am only allowed read-only permission in this repository.

Somehow the ModelSerializer never gets called even though my actuator/beans and actuator/conditions endpoints report the customObjectMapper as a bean. Any ideas why? Do I need any other specifics jackson dependencies?

Here's my dependency tree with jackson dependencies:

com.enterprise.project:spring-webflux-custom-objectmapper:jar:1.0.0
+- org.springframework.boot:spring-boot-starter-actuator:jar:2.6.3:compile
|  +- org.springframework.boot:spring-boot-starter:jar:2.6.3:compile
|  |  +- org.springframework.boot:spring-boot:jar:2.6.3:compile
|  |  |  \- org.springframework:spring-context:jar:5.3.15:compile
|  |  |     +- org.springframework:spring-aop:jar:5.3.15:compile
|  |  |     \- org.springframework:spring-expression:jar:5.3.15:compile
|  |  +- org.springframework.boot:spring-boot-autoconfigure:jar:2.6.3:compile
|  |  +- org.springframework.boot:spring-boot-starter-logging:jar:2.6.3:compile
|  |  |  +- ch.qos.logback:logback-classic:jar:1.2.10:compile
|  |  |  |  +- ch.qos.logback:logback-core:jar:1.2.10:compile
|  |  |  |  \- org.slf4j:slf4j-api:jar:1.7.33:compile
|  |  |  +- org.apache.logging.log4j:log4j-to-slf4j:jar:2.17.1:compile
|  |  |  |  \- org.apache.logging.log4j:log4j-api:jar:2.17.1:compile
|  |  |  \- org.slf4j:jul-to-slf4j:jar:1.7.33:compile
|  |  +- jakarta.annotation:jakarta.annotation-api:jar:1.3.5:compile
|  |  +- org.springframework:spring-core:jar:5.3.15:compile
|  |  |  \- org.springframework:spring-jcl:jar:5.3.15:compile
|  |  \- org.yaml:snakeyaml:jar:1.29:compile
|  +- org.springframework.boot:spring-boot-actuator-autoconfigure:jar:2.6.3:compile
|  |  +- org.springframework.boot:spring-boot-actuator:jar:2.6.3:compile
|  |  \- com.fasterxml.jackson.datatype:jackson-datatype-jsr310:jar:2.13.1:compile
|  \- io.micrometer:micrometer-core:jar:1.8.2:compile
|     +- org.hdrhistogram:HdrHistogram:jar:2.1.12:compile
|     \- org.latencyutils:LatencyUtils:jar:2.0.3:runtime
+- org.springframework.boot:spring-boot-starter-webflux:jar:2.6.3:compile
|  +- org.springframework.boot:spring-boot-starter-json:jar:2.6.3:compile
|  |  +- com.fasterxml.jackson.datatype:jackson-datatype-jdk8:jar:2.13.1:compile
|  |  \- com.fasterxml.jackson.module:jackson-module-parameter-names:jar:2.13.1:compile
|  +- org.springframework.boot:spring-boot-starter-reactor-netty:jar:2.6.3:compile
|  |  \- io.projectreactor.netty:reactor-netty-http:jar:1.0.15:compile
|  |     +- io.netty:netty-codec-http:jar:4.1.73.Final:compile
|  |     |  +- io.netty:netty-common:jar:4.1.73.Final:compile
|  |     |  +- io.netty:netty-buffer:jar:4.1.73.Final:compile
|  |     |  +- io.netty:netty-transport:jar:4.1.73.Final:compile
|  |     |  +- io.netty:netty-codec:jar:4.1.73.Final:compile
|  |     |  \- io.netty:netty-handler:jar:4.1.73.Final:compile
|  |     |     \- io.netty:netty-tcnative-classes:jar:2.0.46.Final:compile
|  |     +- io.netty:netty-codec-http2:jar:4.1.73.Final:compile
|  |     +- io.netty:netty-resolver-dns:jar:4.1.73.Final:compile
|  |     |  +- io.netty:netty-resolver:jar:4.1.73.Final:compile
|  |     |  \- io.netty:netty-codec-dns:jar:4.1.73.Final:compile
|  |     +- io.netty:netty-resolver-dns-native-macos:jar:osx-x86_64:4.1.73.Final:compile
|  |     |  \- io.netty:netty-resolver-dns-classes-macos:jar:4.1.73.Final:compile
|  |     +- io.netty:netty-transport-native-epoll:jar:linux-x86_64:4.1.73.Final:compile
|  |     |  +- io.netty:netty-transport-native-unix-common:jar:4.1.73.Final:compile
|  |     |  \- io.netty:netty-transport-classes-epoll:jar:4.1.73.Final:compile
|  |     \- io.projectreactor.netty:reactor-netty-core:jar:1.0.15:compile
|  |        \- io.netty:netty-handler-proxy:jar:4.1.73.Final:compile
|  |           \- io.netty:netty-codec-socks:jar:4.1.73.Final:compile
|  +- org.springframework:spring-web:jar:5.3.15:compile
|  |  \- org.springframework:spring-beans:jar:5.3.15:compile
|  \- org.springframework:spring-webflux:jar:5.3.15:compile
|     \- io.projectreactor:reactor-core:jar:3.4.14:compile
|        \- org.reactivestreams:reactive-streams:jar:1.0.3:compile
\- com.fasterxml.jackson.dataformat:jackson-dataformat-xml:jar:2.13.1:compile
   +- com.fasterxml.jackson.core:jackson-core:jar:2.13.1:compile
   +- com.fasterxml.jackson.core:jackson-annotations:jar:2.13.1:compile
   +- com.fasterxml.jackson.core:jackson-databind:jar:2.13.1:compile
   +- org.codehaus.woodstox:stax2-api:jar:4.2.1:compile
   \- com.fasterxml.woodstox:woodstox-core:jar:6.2.7:compile

I also have put the code into a git repository to facilitate if someone can help me out and a issue report into spring-boot repository.

You have annotated your application with @EnableWebFlux. This indicates that you want to take complete control of WebFlux's configuration. This causes Spring Boot's auto-configuration of WebFlux to back off. Among other things, this means that it won't configure WebFlux to use the context's ObjectMapper.

You should either remove @EnableWebFlux to allow Spring Boot to auto-configure WebFlux or you should configure its codecs manually so that they use your ObjectMapper.