In the image below, two reactors aren't working because their output is filled due to one of the generators sending plasma back into the reactors. That plasma keeps looping between the reactors and its two closest generators instead of being consumed by the generators down the line. Removing the top right generator breaks the loop and alleviates the problem.
This doesn't always happen and I can't reliably replicate it. The best way I've found is to cut and paste the whole power plant. The platform never tries to consume more power than three reactors can generate. Temporarily breaking the loop a few times seems to fix it permanently.

