In our logs we regularly find the following lines with "W" severity coming from out 3.6 cluster mongos routers:

2018-08-22T09:01:59.913+0900 W COMMAND  [conn13334] mongos collstats doesn't know about: operationTime
2018-08-22T09:01:59.913+0900 W COMMAND  [conn13334] mongos collstats doesn't know about: gleStats
2018-08-22T09:01:59.913+0900 W COMMAND  [conn13334] mongos collstats doesn't know about: clusterTime
2018-08-22T09:01:59.913+0900 W COMMAND  [conn13334] mongos collstats doesn't know about: configServerState

It seems this warning was added in MongoDB v1.8 as reasonable warning against fields that shouldn't be included when executing the command on a mongos router (SERVER-2752), but it wasn't updated to accept the fields for the 'logical time' clock (SERVER-27745) (since renamed "clusterTime") that were added in 3.6.

I see in the v4.0 code it doesn't have this logic any more, but we won't be moving to 4.0 anytime soon. So just for the next minor version in the v3.6 branch could that block of code in the mongo/s/commands/commands_public.cpp file's CollectionStats::run() function be fixed to also ignore the "operationTime", "gleStats", "clusterTime", "configServerState" fields?