Investigating the problem a bit further I found one of the reactors having the rather intriguing temperature negative i (see screenshot). Removing that reactor I could see the other components starting to gain temperature again. (In the end I removed the entire heatpipe network and all attached machines to get rid of the ridiculous temperatures, and after that the game appears to work fine again.)
- Reactor with negative i temperature.png (8.08 MiB) Viewed 4559 times
The issue is perfectly reproducible from the save, and I see no other stability issues. I've placed the character right next to the bugged reactor. It's an old save with lots of hours in it; I've played it since at least 0.16, possibly earlier. Plain vanilla, no mods. I've tried to attach it, but it doesn't appear to be working (it's 111.5 MB and I get an "Error parsing server response" exclamation mark from phpBB). Happy to provide it by some other means.
I've no idea what the cause may be - I was doing something completely unrelated and the reactor setup hasn't been touched for at least a hundred hours at this point. The three other nuclear plants continued to work fine.
I found one similar issue from last year about negative temperatures in heatpipes, but there the save was corrupted, which isn't the case here.
