I have a replicaSet with two servers and I start getting this "scoped connection not being returned to the pool" when I upgraded to 3.6.3 in every 5 minute...

My servers are setup with sync NTP and I m sure they have the sync time correctly

ANY idea what it could cause this... Thank you

2018-03-24T18:14:17.470+0000 I NETWORK [thread7] Starting new replica set monitor for REP-1/server-1:27017,server-2:27017
2018-03-24T18:14:17.476+0000 I NETWORK [thread7] Successfully connected to server-1:27017 (9 connections now open to server-1:27017 with a 0 second timeout)
2018-03-24T18:14:17.478+0000 I NETWORK [thread7] scoped connection to server-1:27017 not being returned to the pool
2018-03-24T18:14:17.478+0000 I NETWORK [thread7] Starting new replica set monitor for REP-1/server-1:27017,server-2:27017
2018-03-24T18:14:17.483+0000 I NETWORK [thread7] Successfully connected to server-1:27017 (10 connections now open to server-1:27017 with a 0 second timeout)
2018-03-24T18:14:17.485+0000 I NETWORK [thread7] scoped connection to server-1:27017 not being returned to the pool
2018-03-24T18:14:17.486+0000 I NETWORK [thread7] Starting new replica set monitor for REP-1/server-1:27017,server-2:27017
2018-03-24T18:14:17.490+0000 I NETWORK [thread7] Successfully connected to server-1:27017 (11 connections now open to server-1:27017 with a 0 second timeout)
2018-03-24T18:14:17.493+0000 I NETWORK [thread7] scoped connection to server-1:27017 not being returned to the pool
2018-03-24T18:14:17.493+0000 I NETWORK [thread7] Starting new replica set monitor for REP-1/server-1:27017,server-2:27017
2018-03-24T18:14:17.497+0000 I NETWORK [thread7] Successfully connected to server-1:27017 (12 connections now open to server-1:27017 with a 0 second timeout)
2018-03-24T18:14:17.500+0000 I NETWORK [thread7] scoped connection to server-1:27017 not being returned to the pool
2018-03-24T18:19:17.470+0000 I NETWORK [thread7] Starting new replica set monitor for REP-1/server-1:27017,server-2:27017
2018-03-24T18:19:17.476+0000 I NETWORK [thread7] Successfully connected to server-1:27017 (13 connections now open to server-1:27017 with a 0 second timeout)
2018-03-24T18:19:17.478+0000 I NETWORK [thread7] scoped connection to server-1:27017 not being returned to the pool
2018-03-24T18:19:17.478+0000 I NETWORK [thread7] Starting new replica set monitor for REP-1/server-1:27017,server-2:27017
2018-03-24T18:19:17.483+0000 I NETWORK [thread7] Successfully connected to server-1:27017 (14 connections now open to server-1:27017 with a 0 second timeout)
2018-03-24T18:19:17.485+0000 I NETWORK [thread7] scoped connection to server-1:27017 not being returned to the pool
2018-03-24T18:19:17.486+0000 I NETWORK [thread7] Starting new replica set monitor for REP-1/server-1:27017,server-2:27017
2018-03-24T18:19:17.490+0000 I NETWORK [thread7] Successfully connected to server-1:27017 (15 connections now open to server-1:27017 with a 0 second timeout)
2018-03-24T18:19:17.493+0000 I NETWORK [thread7] scoped connection to server-1:27017 not being returned to the pool
2018-03-24T18:19:17.493+0000 I NETWORK [thread7] Starting new replica set monitor for REP-1/server-1:27017,server-2:27017
2018-03-24T18:19:17.498+0000 I NETWORK [thread7] Successfully connected to server-1:27017 (16 connections now open to server-1:27017 with a 0 second timeout)
2018-03-24T18:19:17.500+0000 I NETWORK [thread7] scoped connection to server-1:27017 not being returned to the pool