Accessing Microsoft Teams using organizational or personal credentials
I want to provide some information that will hopefully help other folks having this same issue. Through our own reverse engineering and with info Matt Slomka and other Microsoft Engineers provided from our support case we figured out what our issue was. For starters with the introduction of version 5 the MTRs will try to run "New Teams" if they have the app installed and the required WebView 2. You can tell if your MTR is running new Teams if it has the QR code on the main screen and you haven't specifically set a setting to disable that. Prior to 5.2.115 it was able to fall back to using Old Teams but the 5.2.115 requires New Teams only and if it can't run it this is when you will see this problem. It installs New Teams as a separate MSIX package. Apparently at some point a setting got pushed from Intune to our MTRs to block non admin installs of app packages. Its interesting that setting did not stop it from updating the normal Teams room app to 5.2.115 but apparently it wasn't able to install this separate MSIX package that installs "New Teams".
This article describes the problematic setting our MTRs had https://petervanderwoude.nl/post/prevent-non-administrator-users-from-installing-windows-app-packages-via-windows-10-mdm/. We are setting the affected devices back to 0 for that setting so they can install the New Teams package and will work on 5.2.115.
Microsoft may very well be correct in saying that it's something in the customer environment in causing this issue. We didn't think we had done anything like that but we had, probably inadvertently by sending a setting from Intune to those devices they should not have received that blocked needed app installs.
You can also look in the TeamsUWP log files on the device and look for errors pertaining to Teams21 and for us it showed that the package was missing.
Brandon