Just a comment here: if you get "multiple warnings of strong magnetic interference", the last thing you should do is to engage RTH, which is a fully-automated flight mode that needs GPS (position) and compass (yaw) to work.
In these situations, you can try to remain in P-Mode and bring the AC back, or - if things get really bad - switch to A-Mode and fly manually. If you don't have experience flying in ATTI mode, just practice when you're not in an emergency situation... ready to switch back to P-Mode if things get out of control.
PS: you need to enable Multiple Flight Modes in the DJI GO app, for A-Mode (and F-Mode) to be available via S1 switch.