Dear Mongo Analyst,

I'm issuing this issue with your team as we couldn't find a root cause that might explain how come last Friday saw a brand new upgraded replica set node
(Mongo 3.0.12 WiredTiger) crashes due to what seems to be a high rise in connections which in turn apparently generated high wait times on locks acquiring.

The above has happened starting 12:00PM on Friday the 24th, as can be seen in the log file enclosed hereby.
And was only "resolved" once this host had to be restarted after the entire application experienced unavailability due to denial of service from this node (memory exhaustion).

As per the application side, they had no significant processes taking place at the time as far as they claim, neither no changes in configuration (connection pool settings etc.)

Enclosed please find is also the replica set configuration and current status.

Note that the hosts generating the high rise in connections are the application hosts rather than the replica set nodes.