> Maybe it's a very precise threshold which triggers the issue. Between Linux and macOS, the site module executes different code paths which produce different GC counters.
> Sometimes, the GC must happen in a very precise line, one line later is too late.

How does this explain it not being non-deterministic on, say, macOS since the same lines of code will be executing each time? Is there a way to force things to happen in a deterministic fashion? (I interpreted the responses to mean that it's non-deterministic even when run on the same machine, so I'm not talking about, say, the differences from running macOS on different machines.)