Generally openssl security fixes do not change API/ABIs. In this case I built the newer release without export ciphers, thought that seems an unlikely cause. Perhaps it was memory corruption. Relay is running on non-ECC CPU, though the system has never exhibited any problems related to memory corruption in the past. Network equipment unlikely--Intel server-grade NIC. Has been running fine since the restart so I'll have to let it go unless it comes back at a future date.