I'm getting huge (15-30 second) stalls when I first add an operator, or change the viewport or any one of a number of other things. 15.357 (and .347 before it). several cores run houdini.exe hard for as long as the stall takes. selecting the same operator then creates no stall and runs fine, until I select some other operator, etc.. seems to happen with any file. opening in 14 seems OK. Any ideas on what might do that?

thanks in advance,
David.

Yes, that node you have in your setup that takes forever is being recalculated.
Turn off the Brain icon.

It could be a different issue to what I've encountered based on you saying it affects every file but when it happens to me I've found copying and pasting my scene from to an empty hip file can fix this.

Bingo.
cut and pasting the whole shebang into a new file resolved it. I can work again!!

thanks for the tip!!!

SESI are often interested in having these hip files on-hand, since they are notoriously difficult to recreate.

Might be worth sending to support, just in case?