Slightly odd one for you all. Does anyone have an idea about why my instant pot's pressure cook fill max would have decreased over time/with use?

For context, twice recently I've cooked recipes that I've cooked numerous times before without any issue, and the pot has failed to seal - just constantly venting stream until it runs out of liquid.

I replaced the silicone ring, checked that there was nothing obstructing the valve etc but none of this helped. However, when I took half of the contents out, the pot sealed and is cooking away fine.

Neither of the recipes go over the Max Fill PC line, and as mentioned above, I've cooked both successfully loads of times in the last few years. Is there anything that might be affecting the ability of my instant pot to seal properly with more liquid? Some cleaning or maintenance that I need to do?