It's an almost 30 year old nearly 500 ton structure subjected to radiation, bombardment by starstuff and debris, the stresses of docking and undocking, of boosts, and of constant heating and cooling as it passes in and out of the sun. Getting a clear picture of the comings and going of gasses is probably not easy.
Also in 2021, Nauka (the cursed Russian module) arrived on the station, and accidentally fired thrusters while attached, fighting against the attitude control of the station, flipping it around 540 degrees and putting a lot of stress that the station wasn't designed for on all the structural parts.
It was surreal to follow when it was happening, NASA was seriously underplaying what was going on and it was up to amateurs with telescopes looking at the station to tell the world that the situation is still ongoing.
This is one of the three major mishaps related to Nauka.
