I have the same problem as App not showing on Second Screen - Overwolf Apps / Rocket League Tracker App - Tracker Network here show. Although the solution there works, but the tracker can not automatically appear on my second screen still appeals to be annoying.
To TRN developers: My second monitor is on the right of my main monitor before, everything seems to be fine and works perfectly. After I switched my set-up to put my second monitor to the left of the main monitor and changed Settings in Windows, the function seems not working anymore. I thought this might a clue for you guys to fix this.