Currently in 3.6 and 4.0, apply_ops_concurrent_non_atomic.js can fail as it checks the opCounters for inserts in collections. However, periodic HMAC key inserts can cause this opCounter to go up. This bug was resolved in
SERVER-14364 but had the backports denied for reasons related to other parts of the ticket. It would be helpful to backport just the jstest fix to 3.6 and 4.0 to get rid of the BF failures.