Hydrogen Engine bugs
When there is no output from the Hydrogen Engine it's still showing the pistons moving and the fan is spinning. This is very distracting as you can't easily tell if it's working or not.
Also there seems to be some problem with it's power distribution or something like that. It does seem to be the lowest priority for electricity - if there is any other power source (reactors, batteries, solar panels) on the grid the Hydrogen Engine doesn't output anything at all (more testing shows this doesn't behave the same every time). And if it's the only power source it's output is twitching all the time and doesn't look very stable.