Question: How many screenshots do you have in your thumbnail panel?
In the folder I was testing when I posted there are now 28. Re-testing as I write with a new empty folder. The 1st capture displayed in the panel just fine. The next 4, 20 to 30 seconds apart didn't display until I changed to a different folder and back again. About 4 minutes later a new capture displayed fine. This was the 1st new capture after the folder change.
Currently I'm up to 10 captures. Now 12.
Here's what it seems to be doing. I go back and forth (using GoTo) between two folders until the last capture (or series of captures) taken is showing in the panel. I go back and forth between the two folders once more and it will immediately (a second or so) display the new capture. Each one after that starts backing up until I swap folders again plus one additional "clean" swap that I know will not show anything new.
Hope this makes sense.
I'm up to 20 captures in the test folder and now the "clean" swap no longer helps either.