c1mcs had died for some reason. Looking at dmesg, I see:
None of the other EPICS processes died. Not sure what to make of this. I was at the PSL table working, and had closed the PSL shutter to avoid MC autolocker trying to keep the MC locked while I was mucking about, but this shouldn't have had any effect on an EPICS process?
Anyway, I just logged into c1sus, stopped and restarted the model. IMC locks fine now.