The following assertion:

Fatal Assertion 16506 at src/mongo/util/net/sock.cpp 348

***aborting after fassert() failure

Got signal: 6 (Aborted).

Occurred while the TLS negotiation started and performed a check in the file descriptor to ensure the socket is not invalid (INVALID_SOCKET).

This seems to be caused by a race condition in the way the socket is closed. This race condition marks the socket as invalid after the Socket::close() method is called. This race condition seems to be very narrow and in very unusual conditions.

The cluster did fail over correctly electing a primary from a 3-member replicaset.

Applications also did heal transparently redirecting connections to the new primary.