I get this message in the log and the plugin won't work after the update.

Should I completely remove the older version before using the lastest?
If yes, it would be nice if it was mentioned in the update news.

¯\_(ツ)_/¯

It's no bug. It's working.
It was because I didn't delete the old files.
I know a rewrite shall give that information but I would
really be happy if developers would write a short message like: "Delete old files!" or something
in the update description.

I didn't tell you to delete your preexisting files because that should have given you the error seen in this thread. No one else has reported this bug, and I was unable to recreate it.

Ok. Thats weird then.
Just overwriting the plugin file led to that error.
Deleting all the files worked.