Android release build stuck transforming .aar file

After modularizing my app, when trying to make a release build, gradle always seems to be getting stuck on transforming a .aar file, though it doesn't for debug builds.

This is the step it gets stuck on, when I do gradlew assembleRelease

Transforming [LibraryName].aar (project :lib:library) with DexingNoClasspathTransform > DexingNoClasspathTransform [LibraryName]-runtime.jar

The .aar file is included in its own module

build.gradle

configurations.maybeCreate("default")
artifacts.add("default", file('[LibraryName].aar'))

This module has nothing else, and is required by a different module.

Everything worked fine, until the time came to make a release build. Can anyone help with this?

I managed to fix it, by changing the way I import it, and by enabling minification.

In settings.gradle, I added

flatDir {
        dirs 'libs'
    }

to

dependencyResolutionManagement {
    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
    repositories {
        google()
        mavenCentral()
        flatDir {
            dirs 'libs'
        }
    }
}

Then in the build.gradle of the module that actually made use of the aar file (rather than a separate module just to import it)

implementation(name: 'AJVoIP', ext: 'aar')

Finally, in build.gradle for :app, I set minifyEnabled to true

release {
            minifyEnabled true
            crunchPngs true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
        }

This in itself solved the problem, but build times were very slow (13+ minutes)

Adding this to gradle.properties reduced build times up a lot.

android.enableR8.fullMode=true