18 tests fail when run in parallel, but succeed when run standalone

[yurivict]

We are getting these failures when the testsuite runs:

99% tests passed, 18 tests failed out of 3582

Total Test time (real) = 1694.23 sec

The following tests FAILED:
        167 - tests/lean/PPRoundtrip.lean (Failed)
        491 - tests/lean/replaceLocalDeclInstantiateMVars.lean (Failed)
        508 - tests/lean/scopedInstanceOutsideNamespace.lean (Failed)
        510 - tests/lean/scopedMacros.lean (Failed)
        1126 - tests/lean/run/983.lean (Failed)
        1142 - tests/lean/run/ExprLens.lean (Failed)
        1151 - tests/lean/run/PPTopDownAnalyze.lean (Timeout)
        1203 - tests/lean/run/async_select_channel.lean (Failed)
        1344 - tests/lean/run/collectLooseBVars.lean (Failed)
        1544 - tests/lean/run/eqnsPrio.lean (Failed)
        2322 - tests/lean/run/letToHave.lean (Failed)
        2342 - tests/lean/run/library_suggestions_mepo.lean (Failed)
        2813 - tests/lean/run/splitIfIssue.lean (Failed)
        2929 - tests/lean/run/tactic_config.lean (Failed)
        2985 - tests/lean/run/try_heartbeats.lean (Failed)
        2989 - tests/lean/run/try_parallelism.lean (Failed)
        2992 - tests/lean/run/try_user_suggestions.lean (Failed)
        3071 - tests/lean/run/whereCmd.lean (Failed)

However, each of them succeeds when run standalone.

There is parallel contention going on that needs to be fixed.

Version: 4.29.0

[nomeata]

We often run our test suite highly parallely, and I have not observed this. Is this on FreeBSD? What is the error reported from the failing tests?

[Kha]

As-is this is definitely cannot-reproduce