"Class not found" error when deploying Symphony to Heroku - php

Question

When I try to deploy my code to heroku (git), my deployment fails with the following error message:
Generating optimized autoload files
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Executing script cache:clear [KO]
[KO]
Script cache:clear returned with error code 255
!! Symfony\Component\ErrorHandler\Error\ClassNotFoundError {#70
!! #message: """
!! Attempted to load class "DebugBundle" from namespace "Symfony\Bundle\DebugBundle".\n
!! Did you forget a "use" statement for another namespace?
!! """
!! #code: 0
!! #file: "./vendor/symfony/framework-bundle/Kernel/MicroKernelTrait.php"
!! #line: 132
!! trace: {
!! ./vendor/symfony/framework-bundle/Kernel/MicroKernelTrait.php:132 { …}
!! ./vendor/symfony/http-kernel/Kernel.php:386 { …}
!! ./vendor/symfony/http-kernel/Kernel.php:786 { …}
!! ./vendor/symfony/http-kernel/Kernel.php:128 { …}
!! ./vendor/symfony/framework-bundle/Console/Application.php:168 { …}
!! ./vendor/symfony/framework-bundle/Console/Application.php:74 { …}
!! ./vendor/symfony/console/Application.php:171 { …}
!! ./vendor/symfony/runtime/Runner/Symfony/ConsoleApplicationRunner.php:54 { …}
!! ./vendor/autoload_runtime.php:35 { …}
!! ./bin/console:11 {
!! ›
!! › require_once dirname(__DIR__).'/vendor/autoload_runtime.php';
!! ›
!! arguments: {
!! "/tmp/build_bdf9f8d3/vendor/autoload_runtime.php"
!! }
!! }
!! }
!! }
!! 2022-08-27T11:43:06+00:00 [critical] Uncaught Error: Class "Symfony\Bundle\DebugBundle\DebugBundle" not found
!!
Script #auto-scripts was called via post-install-cmd
! ERROR: Dependency installation failed!
!
! The 'composer install' process failed with an error. The cause
! may be the download or installation of packages, or a pre- or
! post-install hook (e.g. a 'post-install-cmd' item in 'scripts')
! in your 'composer.json'.
!
! Typical error cases are out-of-date or missing parts of code,
! timeouts when making external connections, or memory limits.
!
! Check the above error output closely to determine the cause of
! the problem, ensure the code you're pushing is functioning
! properly, and that all local changes are committed correctly.
!
! For more information on builds for PHP on Heroku, refer to
! https://devcenter.heroku.com/articles/php-support
! Push rejected, failed to compile PHP app.
! Push failed