Works again when all caches (incl. the Browser) are cleared or the server got restarted.
I ran the update on another website and there it works. Both pages use the same plugins, themes and have the same updates installed.
Yes, the plugin doesn’t work anymore. Showing no feed, just the buttons „Show more…“ and „Follow on Instagram“.
Anyone of the developers had tested this before offering updates to the users?
The server admin told me the cache system didn’t cleared automatically. The folder problem got solved.