Craft 3 forgets plugins Due to problems I had with Craft 3 Beta 23 I switched back to version Beta 22 (I did this a couple of times)

I do this by importing an sql dump of beta 22 and by directly requesting Beta 22 via composer.

The strange thing: Craft forgets about Plugins it had installed. They simply do not appear anymore in the plugins list, although they are installed via composer and nothing changed in them.

I cleared storage/runtime and I also cleared the DB cache via utilities, that does not help.

Any hints why Craft does not show the plugins anymore in the list? Is there another cache?
Craft 3 knows about available plugins via the vendor/craftcms/plugins.php file, which stores info about all Composer packages that were installed with type: craft-plugin in composer.json.

If that file doesn’t exist or is just returning an empty array, then make sure that the craftcms/plugin-installer Composer package is installed, and try re-requiring each of your Craft plugins. As they are (re-)installed, they should get added to plugins.php.