The Auto-sync Deletion Protection is turned on in the AD Sync profile. The AD Sync is not completing due to hitting the threshold
The AD Sync will remove an amount of users from CloudSOC that is larger than the Auto-sync deletion threshold set in the sync profile. Check the monitoring tab to find the AD Sync operation to see what percentage of user are going to be removed. Check AD to verify a larger than normal amount of users are to be legitimately removed. If so, raise the sync threshold to a large enough percentage, then allow the auto sync to complete. Then the threshold can be set back down to the normal amount.