Github workflow hangs at "Job is about to start running on the hosted runner"

This workflow is hung on 2 (or sometimes 3, depending on the attempt) jobs…

where the job raw logs simply say:

2021-10-15T20:36:50.4587474Z Found online and idle hosted runner in the current repository’s organization account that matches the required labels: ‘macos-latest’
2021-10-15T20:36:50.5483254Z Waiting for a Hosted runner in the ‘organization’ to pick this job…
2021-10-15T20:36:51.2211484Z Job is waiting for a hosted runner to come online.
2021-10-15T20:36:58.8122046Z Job is about to start running on the hosted runner: GitHub Actions 5 (hosted)

I don’t think this is an issue with resource limits on our organization since we don’t have a lot of concurrency and these tests run relatively quickly.

It’s been happening since I added a few tests yesterday (this is the commit that I believe should be working for all tests).

The fact that the logs don’t show the hung jobs ever getting scheduled, combined with the fact that the jobs that hang are not the same every time, make me think it isn’t a problem with my tests.

So far in the 4 attempts I made to re-run (both by making new no-op commits and also clicking the “rerun workflow” button), the 2 jobs with windows-latest python 3.7 and 3.8 have always failed, but most of the time all of the other jobs succeeded. However in the current run, the macos-latest for py 3.8 is now hung the same way.

Also, I’ve let past runs go for many hours (10+) before either cancelling to retry (or make some tweaks and retry). These tests run in a few minutes on my laptop (and in the jobs that succeed).

The new tests do use pytest-venv and subprocess to run some shell commands, the first part of which is to activate a virtualenv.