> So, I was finally able to replicate a failure in test_still_running locally, it required using a rather ridiculous number of parallel workers

I forgot to mention that I was able to replicate the above failure on the latest commit to the 3.8 branch. I was _unable_ to replicate the failure on the latest commit to master, even when scaling up the number of parallel workers (the max I tested was 300 workers and ~3k iterations of test__xxsubinterpreters).