Thank you Elvin,
I’ve done as you suggested to no effect. The problem is only visible when I am not logged into WordPress. So I login in incognito mode. It looks fine to me when I’m logged in.
The issue is also very inconsistent. Some categories pages are affected, some are not. Same with the posts. I can fix the posts one at a time by just hitting the update button. It seems to re-set the post. Unfortunately, it doesn’t work with categories.
Cheers,
Margarita