Gas disapeargin from locked room

From time to time when I look into my disinfection room I notice that all the amount of gas goes down. 

It started with 2kg of pressure (I have a normal vent that was working properly). 
I think it was around cycle 700 that I noticed my chlorine and hydrogen where gone, with pressure on micrograms. 

I couldn't tell at what point it was, since I tried to load all the previous autosaves and all had the same issue. 
But I could've sworn that it happened when I loaded the game, since early that day it was all normal (I have to manually allow liquids in there to disinfect) 

I haven't constructed new tiles, and the only pump has a filter for only polluted oxygen. 
Even if it was a leak from constructing, then the oxygen around should have gone in, since the surrounding pressure is about 3kg in some places, minimum of 2.5kg. 

I checked with people on reddit, but couldn't figure out what happened and let it slide filling it up again. 
 

Today it happened again, I opened my game and was focused on others part I'm working on, then I noticed because I have some plants that are stifled from the pressure.  

I'm including the auto save file just before I noticed this (the rest are all the same). 
I can't attach my save here since it's 7.49MB 
I uploaded it to mediafire https://www.mediafire.com/file/uxflnx0lykuix5q/Crater_Cycle_826.zip/file 
 

The room is located around 50 tiles down of the gate