I can't find an open an issue about this, but for a while now we have infrequent failures on MacOS CI due to a heisenbug:

FAILED numpy/linalg/tests/test_linalg.py::TestQR::test_stacked_inputs[float32-outer_size2-size2] - RuntimeWarning: invalid value encountered in matmul

As far as I know, no one has been able to reproduce this outside of CI and no one has been able to reliably trigger it besides running the MacOS CI repeatedly.

Unfortunately, adding free-threaded CI is making this happen more often because we run CI on Mac runners more often.

I'm opening this issue to have a place to link to when I merge PRs with CI failing on this one test and hopefully to attract someone who can figure this out and fix it!