Also had this happen with hydrogen, which would drop to the point where it liquidated! Didn't get a snapshot of that though.
Pulling out all the surrounding pipes and machines seems to fix it, but it pops up all over the place randomly.
This seems to happen especially when a pipe intersects a thin layer of water.
Also the temperature will stop dropping if you save then the game and reload.
Steps to Reproduce
This issue has not been confirmed by a developer yet.