The title says it all but it seems dupes don't clean germs off their hands at the Hand Sanitizer while wearing Oxygen Masks. I haven't tested this with the Wash Basin or Sink but if it works properly with those, I assume this building was just overlooked when the masks were added to the game. If I had to guess, this has something to do with how normal exosuits act as a protective layer against germs, but oxygen mask don't, so the game thinks the dupe's "suit" (the mask) is germ-free and so they don't bother washing their hands while wearing the mask.
This consistently happens whenever a dupe is wearing an oxygen mask, they ignore the hand sanitizer when running past regardless of how many germs are on their hands. Mask-less dupes would use the same hand sanitizers with no issue.