I connect OTG every time no issues by doing the following:
1- turn off phone / tablet wifi
2- turn on RC
3- turn on spark
4- wait for light to go green on RC, then plug in micro usb into RC
5- open DJI Go 4
6- connect OTG to phone / tablet.
Thank you, I'm loving it, got the spark over other drones because I'm travelling Australia so makes life easier than trying to lug any other big bags around!