I added several hundred Olympus raw (.orf) and jpeg files yesterday and left Imatch do it's processing until it was completed.
When I went into those folders today to start the renaming process, none of the .orf files had thumbnails, though they displayed fine in the quick viewer. I had to highlight all of the files and do a Force Update, which is a bit time consuming.
I have the WIC codecs installed and have not seen this problem before now. Is there some setting I need to change so I don't have to keep doing this?
If you have never seen this problem before, what has changed?
Which other software did you run at that time?
Do you create cache files on-demand or during import (Edit > Preferences > Cache)
Did you keep the IMatch log file from that session (log file (https://www.photools.com/help/imatch/#im_logfile.htm)) so we can check if IMatch reported errors or warnings?
As so often with such strange issues, the more info we get, the better.