I was starting to get the following Error after updating a OctoberCMS instance with composer:
PHP Fatal error: Class Illuminate\Cache\FileStore contains 2 abstract methods and must therefore be declared abstract or implement the remaining methods (Illuminate\Contracts\Cache\Store::many, Illuminate\Contracts\Cache\Store::putMany) in ...\vendor\laravel\framework\src\Illuminate\Cache\FileStore.php on line 10 PHP Fatal error: Uncaught Error: Cannot instantiate abstract class Illuminate\Cache\FileStore in ...\vendor\laravel\framework\src\Illuminate\Cache\CacheManager.php:151
After a couple of hours of debugging and testing i found out that this is because of the composer-merge-plugin which installs older versions of the Laravel Libaries. For me the culprits were these two Plugins but the easiest way to debug it is to disable one Plugin after the other until it works.
I hope this helps somebody with the same Problem :)