Unable to shell into mongo db 3.4.24, logs only shows connections accepted

Hi All,

I have a replica set with 2 secondaries in it. All operations are mainly going to primary. Some load on your application cause the DB to completely locked down. No operations are performed in that period. The db log only shows the logs related to accepting connections. Connections goes upto 3000. After 30 minutes or more the DB comes back to normal and starts executing the requests. All the requests show very high times.
timeAcquiringMicros: { r: 3689113995 }
I am not finding the way to debug this issue. In this duration the database locks goes upto 111 seconds (read and writes both).
When I try to shell into the db in this time when db is locked. Shell doesn’t let me inside. It just keep waiting. If shell responds, I can see a db.currentOp to see the operation which blocked the db.

Is there any way to debug such issue.
Please help me to understand how can I solve this issue.