prime raft
Upon accessing a nav station at x4 gamespeed and above (x8 consistently, though I'm still experimenting) causes fusion reactors to stall. This can also occur a second or two after SFFWD at x1 gamespeed.
Will upload a save soon, and edit this as I discover more conditions, but others do seem to be encountering similar issues as well in their saves, including reactor shutdowns on walking between ships.
snow nova
I can second this, with the addition that my reactor also sometimes shuts down when I quicksave while doing interplanetary travel at 4x or above. The problem first started at the end of my trip to Ceres, but I was able to deal with it and make it there. Now I'm trying to fly to Jupiter and I can't get anywhere without my nav console eventually saying something along the lines of "Reactor output changed significantly" and my auto pilot deactivates. After looking at this bug I tested it without speeding up time and I now realize it does only happen to me when the game is 4x or above. It happens if I'm running on 4x and access my nav console, quicksave, or SFFWD. I have a save file to provide but it's too big for discord, it's saved right before I fly to JPTN and the bug is easily reproducible. Let me know if there's some way to get it to you because I'd very much like to check out Jupiter and I feel like this save file could help. Also, my save file also contains the bug mentioned in the "Merga Plot is not advancing", so it could potentially help you with that bug as well.