I had the same Bug with just one Shower but two other Water needing Buildings in the Pipeline before the Shower. I think the base Problem is that the Shower doesn't store the Water and the Pipes don't supply it fast enough. The Shower says "not pumping" for a second after a Dupe finishes showering early.
I have a closed Pneumatic Door with Water, Dirt, etc behind it. Dupes still try to do Jobs that require them to pass through the Door. This leads to Dupes just standing in front of the Door. Since is just closed the Door recently the Jobs might have been assigned before the Door was closed.