TLDR: New Group Series 500 is able to use the “Join” button for SfB meetings created by users with video call features enabled but cannot join SfB meetings created by users without the video call features enabled.
I have a New Group Series 500 (Hardware rev - 18, Release - 5.1.2-320034) that has registered with no issues to on prem SfB 2015 and Exchange servers. The calendar for the room shows up and can join some users Skype for Business meetings.
The issue I am having is when a user that does not have the video calling features enabled for their SfB account makes a Skype meeting and invites the room with the Group Series 500 it will not stay connected. In the desktop SfB client the room will show up briefly then automatically disconnect. The Group Series will show an error that “The call was rejected for unknown reasons” or something along those lines. When trying to add the room manually in the SfB client it will behave the same way. Enabling video for all users is currently not an option due to network load.
I am unsure of the relevance but we have had a Trio 8800 with Visual+ and Skype license that is registered to the same servers running for a few months with no issues.