Thanks Otto, but I found the solution.
The clue to it came from this thread: Version 1.18.9.2571 - killed my windows 10 64bit plex server
My system has multiple versions of the C++ redists on it. After seeing that thread I thought I’d take a chance and reinstall the 2019.
It worked like a charm. All is back to normal with the latest server version.
Don’t know why I had different symptoms from those described in the other post. Maybe because I already had the latest redist installed when I upgraded? Whatever it was it’s fixed now and I’m happy. Four streams so far today and the i7 hasn’t touched 50C yet. All’s well.
Thanks for keeping such a tight eye on problems for us!
Cheers.