Additional information: now I activated the Embed Plus YouTube WordPress Plugin again. The Youtube videos are shown correctly. Only now the admin dashboard isn’t available. So I currently always need to deactivate this plugin in order to be able to access the admin dashboard.
Additional information: currently I disabled all add-ins through phpMyAdmin and actived them one by one in order to be able to access the admin dashboard. I currently kept the Embed Plus YouTube WordPress Plugin deactivated.
I don’t know whether this issue occurred only with the latest update or already earlier, but in general I always try to keep everything up-to-date.
