Thank you Danyer, unfortunately email notifications work erratically for me, dunno why, so I noticed your reply only accidentally !
I tried disabling the Thread Search plugin and now I am testing.
I am not sure, chances are those "hiccups" improved a lot, but I have the impression there are still minor ones while moving the cursor thru the text.
Unfortunately, as I said in my topic, I cannot say for sure from which NB this problem started occurring, so one can't even file a report, but surely it happened somewhere between Spring and August 2024