Hi All, We upgraded our sharded cluster a few days back from 4.2 to 4.4, After upgrading to 4.4, our queries are taking much longer and performance continues to deteriorate. Our sharded cluster configuration:
Instance type: M5.xlarge (data nodes), t3.medium (Config servers)

Shards: 9

Replica set type: PSA

Config Servers: 3

Mongos's: 21

One thing we noticed is when there are less number of mongos's, the performance is much better, but enabling more mongos's leading to performance deterioration. 

We did notice this issue has some similarity to https://jira.mongodb.org/browse/SERVER-51104

Thanks for your help in advance