Glad you got it figured out! As usually happens, there was something else going on. Makes sense, these apps take a lot of resources and sharing with Bluetooth apparently was too much! So so hope you enjoy it and, again, do yourself a favor and read the manual. Double check the parts about straight and curved paths and how those 2 setting affect what happens at waypoints. That has come as a surprise to many.
Interesting, I had similar problems at one stage with Dji Go app on IPad mini 3 16Gb. Turns out it was running out of memory - I cleared off some old videos, closed all unused apps & it worked. Is it possible you are running out of memory too? (Shutting off Bluetooth may be just freeing up enough resources)
I've used my Phantom 4 with my iPhone 6s, my iPad Mini 4, and my iPad Pro, all with wifi and Bluetooth up and running. No issues. I did have an issue with my iPhone 6s crashing with Litchi. It turns out that I was getting a huge battery drain during a mission. If I flew with the phone at less than about 40% charge, it would suck the juice down to the point where the phone saw no battery left and just shut down. It was weird. When I rebooted the phone, it would show 30-40% battery again.