With the latest update (including the pipe re-work), I'm seeing a situation where it seems like gas packets in a pipe are being overwritten by new packets (pushed in via a pump).
See attached video, paying particular attention to the lower left, right at the start. It seems like packets coming from the left-hand pump are literally overwriting themselves waiting for space behind packets from the right-hand pump. It's less obvious when it's O2 overwriting O2 but you can see cases where an H2 packet just disappears (and then no new H2 ends up in the top mechanical filter).
The only case where you can see H2 actually making it out is if the H2 packet originates in the right-hand pump. Any from the left-hand pump are disappearing while waiting.
Have 2 gas pumps feeding into a single pipe going into a bridge.