Hi. I had this issue. I found out that when I remote desktop connection to the raspberry pi 3 and try to open Teamviewer Host I have the same problem as you. But I found out that what in reality happens is that teamviewer opens on the main session, that is, the one that I can see if I plug in a monitor display to the RPI3 (I'm not really sure if I'm describing it well, but what remote desktop connection seems to do is open a new session) So try logging in to that main session and see what happens, it should work there. Hope this helps.
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