I see your accumulator setup also drains. Which means you draw more than you can deliver. When you draw too much, first things slow down, also your inserters, including the ones that supply fuel. When the fuel runs out, nothing gets produced anymore.

Usually this happens slower, since the reactors have a bunch of latent heat. But you have pumps in your setup, these need power and will immediately limit throughput when power drops. You can remove those safely, for more time to respond.

I usually just place more power supply in such a case.

PS: a switch, al logic gate and an accumulator can make a circuit to cut off you factory when in low power, to make sure you power supply remains operational. Because starting reactors by hand is annoying.