I don't understand it either, Al. No part of the system is above the water line.

When I checked the skimmer sock that day It was full of bracts and soggy pollen. Is it possible that it was so clogged that not enough water went through the skimmer into the pump? I've kept an eye on it these past 2 days and have changed skimmer socks twice daily, and the issue seems to have resolved itself. The pot is filled completely and has its normal small bubble directly in the center of the domed lid. I can't help but think the pump was starved for water when the sock was dirty.