Because of SERVER-41185 (introduced in 4.4), a mongos / mongod will not start if FTDC fails, such as unable to create the dir due to permission issue.

In v4.2 and older, the failure would be non-fatal allowing the MongoDB process to function.

This change in behaviour should be mentioned in the documentation. This seems to be the most appropriate place:

https://docs.mongodb.com/manual/release-notes/4.4-upgrade-sharded-cluster/