The SMTP availability of the Receive connector

Hi All,

After migrated to exchange 2013, everything has been working fine for about four weeks than, suddenly  below warning message started to get logged every 15 min in the Event log... Email flow is still OK, no updates or any other changes have been done on the Server. Any help would be greatly appreciated.

Exchange 2013 CU8  Mailbox Server  + CAS Server running on the same Hyper-v VM.

The Event Details  “The SMTP availability of the Receive connector Default Mailbox Delivery was low (0 percent) in the last 15minutes."

Tried to increase the mailbox deliveries throttling values by following commands. issue still there

Set-MailboxTransportService -MaxConcurrentMailboxDeliveries 50

Set-TransportService -MaxConcurrentMailboxDeliveries 50

Issue is still there?

Thank you in advance.