docker-compose+laravelにて環境構築時にエラー

前提・実現したいこと

docker-compose+laravelでの環境構築しております。
コンテナの構築までは完了したのですが、ワークスペースサーバ内にてcomposer installを実行したところ下記のエラーが発生致しました。

依存関係の問題なのかと思うのですが、具体的な問題箇所の特定ができない状況です。

原因箇所の特定や、こういった状況での問題の特定方法などお知恵を拝借できればと思います。

発生している問題・エラーメッセージ

PHP Warning:  Uncaught ErrorException: require(/var/www/vendor/composer/../../app/helpers.php): failed to open stream: No such file or directory in /var/www/vendor/composer/autoload_real.php:66
Stack trace:
#0 /var/www/vendor/composer/autoload_real.php(66): Composer\Util\ErrorHandler::handle(2, 'require(/var/ww...', '/var/www/vendor...', 66, Array)
#1 /var/www/vendor/composer/autoload_real.php(66): require()
#2 /var/www/vendor/composer/autoload_real.php(56): composerRequire5ca5401772281cd62db5a40c315283f1('4287f956e84093f...', '/var/www/vendor...')
#3 /var/www/vendor/autoload.php(7): ComposerAutoloaderInit5ca5401772281cd62db5a40c315283f1::getLoader()
#4 /var/www/vendor/laravel/framework/src/Illuminate/Foundation/ComposerScripts.php(43): require_once('/var/www/vendor...')
#5 phar:///usr/local/bin/composer/src/Composer/EventDispatcher/EventDispatcher.php(282): Illuminate\Foundation\ComposerScripts::postAutoloadDump(Object(Composer\Script\Event))
#6 phar:///usr/local/bin/composer/src/Composer/EventDispatcher/EventDispatcher.p in /var/www/vendor/composer/autoload_real.php on line 66

Warning: Uncaught ErrorException: require(/var/www/vendor/composer/../../app/helpers.php): failed to open stream: No such file or directory in /var/www/vendor/composer/autoload_real.php:66
Stack trace:
#0 /var/www/vendor/composer/autoload_real.php(66): Composer\Util\ErrorHandler::handle(2, 'require(/var/ww...', '/var/www/vendor...', 66, Array)
#1 /var/www/vendor/composer/autoload_real.php(66): require()
#2 /var/www/vendor/composer/autoload_real.php(56): composerRequire5ca5401772281cd62db5a40c315283f1('4287f956e84093f...', '/var/www/vendor...')
#3 /var/www/vendor/autoload.php(7): ComposerAutoloaderInit5ca5401772281cd62db5a40c315283f1::getLoader()
#4 /var/www/vendor/laravel/framework/src/Illuminate/Foundation/ComposerScripts.php(43): require_once('/var/www/vendor...')
#5 phar:///usr/local/bin/composer/src/Composer/EventDispatcher/EventDispatcher.php(282): Illuminate\Foundation\ComposerScripts::postAutoloadDump(Object(Composer\Script\Event))
#6 phar:///usr/local/bin/composer/src/Composer/EventDispatcher/EventDispatcher.p in /var/www/vendor/composer/autoload_real.php on line 66
PHP Fatal error:  composerRequire5ca5401772281cd62db5a40c315283f1(): Failed opening required '/var/www/vendor/composer/../../app/helpers.php' (include_path='.:/usr/share/php') in /var/www/vendor/composer/autoload_real.php on line 66

Fatal error: composerRequire5ca5401772281cd62db5a40c315283f1(): Failed opening required '/var/www/vendor/composer/../../app/helpers.php' (include_path='.:/usr/share/php') in /var/www/vendor/composer/autoload_real.php on line 66

補足情報

コンテナの状況。
$docker-compose ps
|Name|Command|State|Ports|
|:--|:--:|--:|
|testprj_docker-in-docker_1|dockerd-entrypoint.sh|Exit 2||
testprj_laravel-echo-server_1|npm start|Up|3000/tcp, 0.0.0.0:6001->6001/tcp|
|testprj_nginx_1|nginx|Up|0.0.0.0:443->443/tcp, 0.0.0.0:80->80/tcp|
|testprj_php-fpm_1|docker-php-entrypoint php-fpm|Up|9000/tcp|
|testprj_postgres_1|docker-entrypoint.sh postgres|Up|0.0.0.0:5432->5432/tcp|
|testprj_redis_1|docker-entrypoint.sh redis ...|Up|0.0.0.0:6379->6379/tcp|
|testprj_workspace_1|/sbin/my_init|Up|0.0.0.0:2222->22/tcp|