We need to know what happened to the act_log table, how it was possible that historical records were deleted from that table, and if the records can be restored.
Service Desk Manager 17.x
In reviewing the stdlog we found a 45-minute window where the act_log table could not be found by Service Desk. After this time period, the error messages went away and the act_log appeared to have returned.
We concluded that for an unexplained reason, and outside the scope of what Service Desk Manager can control, the act_log table had been accidentally dropped from the database, and then restored from a backup. When restoring the table, any records that were created after the backup was taken and before the table was restored were lost and cannot be recovered.