This typically indicates a communication problem. I doubt it is related to the upgrade.
Aso, the event message may be expected if one of the Exchange servers is down or if you are in a DAG and there is no mailbox on a given server (the archiving task for that server may generate these events).
Another thing I can think of is that it may be related to a problem with the EV service account credentials. Have a look at this article as well: https://www.veritas.com/support/en_US/article.000086203