Initializing a new replica set configuration (especially the case of a member removal) can occasionally cause a crash on one or multiple running members of the replica set. The members which incur a crash may be safely restarted.
Crashing replica set members affect quorum and can in the worst case lead to no primary and unavailability of the replica set.
If a member is being removed, shutting it down prior to its removal from the replica set configuration will reduce (but not eliminate) the chance of a crash. For the case where a member is not being removed, no known workaround is available.
The replica set handshake handler was fixed to be resilient to the receipt of handshakes while initializing a new replica set configuration.
Version 2.6.0 is affected by this bug.
The patch is included in the 2.6.1 production release.