Worked! Thank you so much for helping out!
I found out that the problem – on my site – was caused by the WP 301 Redirect plugin. I replaced it with the popular ‘redirect’-plugin and then all was fine.
I have the problem that I cannot enter anything in the ‘focus keyphrase’ field (or only very slow), nor can I delete its content (when a post has been copied) and there is a wheel endlessly turning at ‘readability’. But no result comes up.
This has been going on for some time but the last weeks it has become a real nuisance, as there is no way around. Before at least wirh a lot of patience, I was able to edit the field.
Avada, (Free) Yoast plugin, Safari on a IMac. All latest versions.