The /sessions/unified/snapshot-sessions JSON spec test currently fails and/or is flaky. The specific sub-test that fails is "countDocuments operation with snapshot". It produces this error:

error: checking expectResult:  { "$numberInt" : "2" }

The test is currently being skipped, so to work on it, it will first be necessary to remove it from .evergreen/skip-tests.txt and run a patch build to determine the current failure mode(s).