Analyzing all the posts it seems to be that the Samsung S7 and Android Nougat are mentioned quite too often. Very likely to be avoided especially in combination.
The S7 seems to be the only Samsung Android device not all but many owners complain about in other posts as well. Its a great smartphone with high specs otherwise.
I have used for several years IOS devices and found them exceptional for Drone operation. If someone has trouble with Android driven devices get an Ipad
Mini 2 which are cheap now
and very likely you will be just flying instead of posting about your very valid disappointments .
I still decided to switch to Android devices for many good reasons.
Never forget Android is an operating system only. It can run on cheap $ 80.00 low spec phones or on high spec phones or tablets. That is the beauty of Android.
Everyone can have access to the features without breaking their individual bank accounts.
However, when you experiment with a low spec Android device and play Youtube or play back video in general its not that smooth. Playing certain games on low spec Android
devices are no fun. Same for Flying DJI drones. You need high spec devices with Snapdragon CPUs, high amounts of ram and fast Mali GPUs. You have to be on par with the high spec devices of Apple which show no problems. The reason why Apple sticks out is because they only produce high spec devices. Extremely fast processors, good amounts of ram and the exceptional OS.
On Android devices you can not have apps in the background like email, whatsapp, facebook and others trying to update all the time or apps hunting for upgrades. You need to kill all possible interference sources and best is to switch the phones to flight mode. These phones are designed for multitasking, when you fly you want all technical ability of the phone focused on your drone flight.
I have now four devices running Android 6 and they are as stable as the mini Ipad I borrow at times from my daughter. Its a Samsung Note 4, a Xiaomi MiMax with a beautiful 6.4 inch screen
and 3 gb ram, a Samsung S2 tablet and a Nvidia K1 tablet. All very different devices and all run extremely flawless on DJI Go4, Litchi and DJI Ultimate Flight which has better features than
Litchi. This is on .600 firmware and Android 6. They also worked fine before on .400 firmware and/ or on Android 5.
If you have problems with the apps, try uninstalling and re installing them. It has made a huge difference for some users. If you run Android 7 and have unidentifiable issues you might be better off to downgrade to 6. If you have disconnects of the apps, check for apps running in the background and change the USB cable. A bad cable causes disconnects.
If you have a Samsung S7 and problems try .400 firmware and Android 6. If there are still problems and makes your drone flight hobby a misery get a reasonably priced IOS device. It will bring the fun back into Drone flying and you can still enjoy an otherwise great smart phone.