https://spruce.mongodb.com/task/mongo_node_driver_next_windows_64_vs2019_fermium_test_4.2_replica_set_7199d26a51b47a546da9fa0d21d26eb01e4fdfd2_23_05_16_20_47_51/tests?execution=0&sortBy=STATUS&sortDir=ASC

Notes:

I can confirm it's not a code change that has caused the failures. I restarted previous passing builds on the waterfall and they fail now with the same error.

It's definitely related to mocha - the error changed to the first mocha parameter that I passed to it in the "check:test" script when trying to get more debug. So previously the "-config" is now "-full-trace" when I was trying to get a real stack trace out of the error. That obviously didn't work as I still don't know where it's originating from exactly.

The mocha suite does actually run, and passes.

The Node 14 version has not changed. (14.21.3 before and after)

The npm version has not changed (6.14.18 before and after)

I do not see anything out of the ordinary in setup - no errors.
It's only on the "check:test" script - no other scripts get this error.