Thanks Kirk
You'll recall I've been having collection problems of various kinds for quite a while. Your new builds have brought them down to 'liveable with' status but they've not gone away entirely. The collection counts are now mostly, but not always, correct. A few days ago the selection counts bottom left of the contact sheet were showing all files selected when only a subset was. Screenshot.
I'm on a moderately upgraded Mac Pro running 10.14.6. I wonder if there's something about this setup that upsets whatever does the counting in PM+?
David