We have the same problems with the calender on several of our rooms after upgrading to 4.8.31.0. Teams Admin Center keeps reporting that the room isn't connected to Exchange. Our MTR accounts have on-prem Exchange and TeamsOnly.
After i tried to reset the MTR app the Event log keeps spamming: "We can't sign you in because the server couldn't be reached or the server version is incompatible with the device. Contact your support team with this information." - this is for Skype, Teams works like normal.
Microsoft have also deployed 4.8.31.1 of the MTR app, but the relase notes isn't updated yet. https://docs.microsoft.com/en-us/microsoftteams/rooms/rooms-release-note#48310-05122021
Sohail_Tariq and Ilya Bukshteyn do you have and information about the 4.8.31.1 release?
4.8.31.1 or the latest available version can be downloaded from this link: https://go.microsoft.com/fwlink/?linkid=851168