You may have experimented a downtime affecting the operation of the synchronization Middleware.
It occurred on the period between 2019-06-13 17:00 CEST and 2019-06-14 09:00 CEST, a temporary interruption of the synchronization between ACRM and ACM systems was experienced. Customers with ongoing email campaigns during this period might have experienced a delay in the reception of results in ACRM.
The problem is resolved and all pending messages were made available to ACRM without any loss of data.
Please do not hesitate to contact the Support if you have any question.