IMC was not locked for the past several hours. Turned out MC autolocker was stuck, and I could not ssh into megatron because it was in some unresponsive state. I had to hard-reboot megatron, and once it came back up, I restarted the MCautolocker, FSS slow servo and nds2 processes. IMC re-locked immediately.
I was pulling long stretches of OSEM data from the NDS2 server (megatron) last night, I wonder if this flakiness is connected. Megatron is still running Ubuntu12.