It appears that Conlog had stopped running at around 15:16. The following error was logged:

Dec  9 15:16:54 h1conlog2 conlog: ../conlog.cpp: 301: process_cac_messages: MySQL Exception: Error: Out of range value for column 'value' at row 1: Error code: 1264: SQLState: 22003: Exiting.
Dec  9 15:16:55 h1conlog2 conlog: ../conlog.cpp: 331: process_cas: Exception: boost: mutex lock failed in pthread_mutex_lock: Invalid argument Exiting.

I've restarted it for now.