AC has an aircraft status diode, and Radio Link status diode.
RC has a diode which tells link status as well.
Status diodes are identified and explained, of course, in the manual.
You can control the AC without the app, so one way forward would be to focus on the RC and AC.
But if you consider mobile device link more important, it is possible to start with this one as well - connection to RC doesn't require the aircraft, it will show "Aircraft disconnected" but you should be able to see RC status, ie. stick positions in options. First, rule out the cable and the mobile device config being the issue.