Hi Ben,
We are new to Newline boards too.
We have been having the same issues.
We have just found out that it is due to the Newlines being powered off when the user sets up their powerpoints to be viewed in Presenter View ad have started the powerpoint before turning the board on.
Due to the setting being ticked it automatically sets the board to duplicate, when they escape the powerpoint or move to a new PowerPoint without Presenter view or a webpage it goes to "PC Only" they then have to Win Key and P to duplicate to get this working again.
It is like PowerPoint is blocking the signal for a secondary screen being attached.
Have you managed to resolve the issue?