So to get it straight; you have a powerbank that you connect to the side USB connector of the RC controller and then connect the display to the bottom USB port of the RC controller?
Do you need some setting for that? Whenever I left the (not to a display/device connected) cable in the side connector while I use the bottom USB port to connect with a tablet/phone, then the app on the tablet/phone would not see the connected mavic. The RC controller would say "ready to go", but the tablet would not.