I agree 100% with what I think is the key phrase, viz. "the results can change without any modification to your code".

I maintain an R package that is quite stable and is widely used. But every month or so, the GHA on one of the R testing machines will report an error. The messages being quite opaque, I typically spend a half hour trying to see if my code is doing something wrong. And then I simply make a calendar item to recheck it each day for a while. Sure enough, the problems always go away after a few days.

This might be specific to R, though.