When you try to access Calendar by using Microsoft Teams, there can be a performance issue that's caused by an incorrect EWS URL and failures can occur randomly.
Autodiscover v2 isn't site-aware in Microsoft Exchange Server 2019 and Exchange Server 2016, so it doesn't always report back the URL for the endpoint that's in the same Active Directory site as the mailbox. Microsoft Teams Calendar in hybrid mode is using Autodiscover v2, which causes Microsoft Teams to fail to display calendar randomly.
To fix this issue, install one of the following updates:
Learn about the terminology that Microsoft uses to describe software updates.