This seems like it has to be caused by DM-27178. But I see Jenkins passed on that branch at 2020-12-16T04:11Z (a force-push thereafter did not significantly change the code), and the nightly lsst_distrib Jenkins build also passed.

The weird thing is that (on lsst-devl02) pytest seems to succeed, as does scons -j 1, but scons -j 8 fails. 20 runs of pytest -n 8 tests/test_cameraMapper.py separated by rm -rf .pytest_cache gives 2 passes and 18 failures. 20 similar runs with -n 4 gives 14 passes and only 6 failures. Interestingly, -n 5 gave 20 failures, and -n 3 gave 19.

Is this a race condition having to do with the Filter singleton?

But the pytest workers run in separate processes, so I don't see how that happens.