[SOLVED] Autoloaded php code not updating after edits inside of Lando environment

The crux of the issue is that I edit a code file and the change does not take effect until after I rebuild my entire environment. Weird thing is that I haven't been having this issue for months of development so far. I just decided to dust off this project and work on it this week and all of a sudden editing files no longer works (without a rebuild).

I don't even know where to begin to try and tackle this. Any advise helps, especially from people who have experience with Lando and Docker. Alright, so because I don't have any idea what's causing this, I'll just try and explain my whole set up and go from there:

I'm using Lando to run a container which is running PHP 7.3. When I SSH into the running container and execute my script php worker.php my script runs no problems. Then if I edit it, say to add a var_dump('hello world!'), I get the expected output. However, if I edit an autoloaded class file, say MyClass.php, and add a var_dump there, nothing happens. In fact I have to completely rebuild the environment with lando rebuild in order to get the var_dump to show up. Weird right?

Ok so here are some things I've tried:

I've tried restarting Docker.
I've tried restarting my computer.
I've tried lando destroy and lando rebuild to start fresh.
I've tried SSHing into the container and running cat mylib/MyClass.php and I see the added var_dump statement!! However when I run php worker.php the var_dump added to MyClass isn't there. How can it be present in the filesystem, yet absent during execution? This is really throwing me for a loop.
I've tried renaming MyClass.php to MyClass2.php and this fixes the issue ONCE. I.e. after it updates I then need to rename it again and again each time there is a change. This obviously isn't a real solution, but it's food for thought.
I've tried manually loading classes using include_once. This works perfectly, edits take effect as soon as they happen. The problem is that I don't want to manually include all my files, I want to use the composer autoloader. I've been using it for a long time, I'd prefer to just fix whatever has suddenly gone wrong with it.

Ok lastly, some theories of mine:

Something is obviously caching stuff but I have no idea what. I thought maybe it was something to do with the PHP Opcode caching, but I, to my knowledge, don't have php opcode caching enabled.
Another theory is that maybe the filesystem mount isn't working. It is working, however, because when I edit worker.php the changes are instantly there each time. This would not be happening if there was no filesystem mount.
One more theory is that either Docker is caching something somehow (I have no idea how), or maybe Lando is? I don't know Lando inside and out. Maybe it has some sort of caching scheme I'm not aware of.
Last theory is that somehow autoloaded classes are cached by PHP itself or my composer or something like that. I also don't know how this is possible, but I'm not an expert on the inner workings of composer or php so if there is a code cache involved here somewhere I'm not aware of it.

So some things I know people might ask for: Dockerfile

FROM php:7.3-apache

RUN apt-get update \
    && apt-get install -y \
       git \
       zip \
       unzip \
       libzip-dev \
       libxml2-dev \
       libssl-dev \
       libc-client-dev \
       libkrb5-dev \
    && docker-php-ext-configure imap --with-kerberos --with-imap-ssl \
    && CFLAGS="-I/usr/src/php" docker-php-ext-install zip mysqli pdo pdo_mysql xmlreader imap

RUN curl --silent --show-error https://getcomposer.org/installer | php
RUN mv composer.phar /usr/local/bin/composer

# Bake composer dependencies into the image for production
WORKDIR /app

COPY composer.json ./
COPY composer.lock ./

RUN export COMPOSER_ALLOW_SUPERUSER=1 && \
    composer install --no-scripts --no-autoloader --no-dev

COPY . ./

RUN export COMPOSER_ALLOW_SUPERUSER=1 && \
    composer dump-autoload --optimize && \
    composer run-script post-install-cmd

COPY vhost.conf /etc/apache2/sites-available/000-default.conf

RUN chown -R www-data:www-data ./ && \
    a2enmod rewrite

EXPOSE 80

.lando.yml

name: mysite
env_file:
  - .env
proxy:
  appserver:
    - mysite.lndo.site
  database:
    - db.mysite.lndo.site
services:
  appserver:
    type: compose
    services:
      build: .
      command: apache2-foreground
  database:
    type: mysql
    portforward: 3306
    creds:
      ---super secret---

composer.json

{
    "name": "MySite/MySite",
    "description": "Would work great if not for caching issues. :(",
    "type": "project",
    "require": {
        "ext-json": "*",
        "ext-imap": "*",
        "doctrine/orm": "^2.6.2",
        "doctrine/migrations": "^2.0",
        "zbateson/mail-mime-parser": "^1.1",
        "rct567/dom-query": "^0.7.0",
        "sabre/xml": "^2.1",
        "phpmailer/phpmailer": "^6.0"
    },
    "autoload": {
        "psr-4": {
            "MySite\\": "./lib"
        }
    }
}

Update: I've found that by deleting vendor/symfony/console and then running composer install it seems to clear the cache. I wish I could figure it out from here, but the answer still eludes me. What does symfony console have to do with autoload caching code?? I have no idea.