Quote Originally Posted by defragster View Post
So far only Windows 10 and multi Teensy has shown trouble AFAIK.
Has the problem ever happened with multiple Teensy boards, but only 1 instance of the Arduino IDE running? (and the hassle of having to repeatedly switch which board you're using in the menus)

My understanding is this looks like a problem from running more than 1 instance of the Arduino software, rather than how many Teensy boards you have connected.