I checked out some other forum posts about the Gas Pump and followed a suggestion to restart the game. Now the setup is pumping Hydrogen into the generator but oxygen is stuck in the Gas Pump. It seems like the Gas Pump has troubles with a mixture of gases.
I've been playing around with Electrolyzer/Hydrogen Generator setups. I rushed my way to Gas Filters and connected all the dots but oddly enough the setup doesn't work. The 'unfiltered' pipe (Which should only contain oxygen in this case) seems to work fine but the Hydrogen seems to be stuck in the Gas Pump. It's hard to tell if this is an actual bug or if I just failed to setup this type of system correctly. See attached screenshots for details