on Feb 28, 2018 at 4:32:41 pm Last Edited By Bill Davis on Feb 28, 2018 at 6:17:08 pm
Those look like the temp files X makes during it's optimizing and proxy processing process. (say that three times fast!)
They should be auto-deleting when the transcode is complete.
Are you force quitting out of some of your transcodes before they are finished?
It's important to let X finish background processes, so you might want to develop the habit of keeping the Render Manager open when you're importing, optimizing or transcoding so you know when the work is complete.
One way this "suddenly starts happening" is when you hit Command Shift Period when you're looking for a different keyboard command. That combination toggles Show/Hide hidden files on and off.