Once you have deployed Microsoft Teams to a user's computer, some may not receive the call notification when an incoming call is being received.
However, they do receive incoming chat message notifications. Why this may happen lies in the local machine configuration. Chat message notifications use text and static content that is delivered by low end graphics.
The Microsoft Teams call notification requires more graphics for animation and the ability to interact with the accept or decline buttons inside.
The problem may be the Graphics Driver on the local machine is out of date and requires updating. Please update the Graphics driver to the latest manufacturer supported version and reboot the device. After this the call notification should work.
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