EDIT: I noticed that I can't change any setting anymore! It just resets after save to the old value. No error message is shown.
Old Title: Theme does not change, even though database value changes If I change the theme in Content -> Design -> Configuration
Then it always changes back to the old theme even though I can see that the value is changed in the database. (Table "core_config_data" -> path: "design/theme/theme_id")
If I reload the frontend, then it still loads the old theme though.
How can I fix this bug? I already cleared the cache with
php bin/magento cache:flush