"ms-diagnostics: 15007;reason="Exchange Unified Messaging server did not respond to request"
"ms-diagnostics: 1038;reason="Failed to connect to a peer"
"ms-diagnostics: 15030;reason="Failed to route to Exchange Server"
However, Exchange calendar integration continues to work on the LPE and VVX phones. This suggested that UM integration was failing because of an recent attempt to update the Exchange 2013 server to CU2. That update failed during prerequisite checks with an error message saying that there were one or more Exchange 2010 servers in the organization that has not yet been updated to SP3. However the Exchange 2010 Edge transport server was already running SP3 so it was unclear why this message appeared. To resolve this issue, I performed the following steps:
1. Remove the Edge Subscription on the Exchange 2013 server using the cmdlet
Remove-EdgeSubscription - identity <edgeservername>