I have a perfect network with no drop out on any app or any device.. My Galaxy S7 phone is actually great with every other app I throw at it.
My system is BT infinity 80.b. Netgear router. DLink switch. Audioquest cat7 Ethernet cable. Galaxy S7 control.. Naim NDX. Latest firmware. Qnap NAS. (NEW)
However the Naim app is slow. Dreadfully slow to browse between folders. (I only use folder view)
I would pay a lot of money just to understand what the issue is. If I use Bubble or indeed Qnap's own apps on my phone they are like lightening. The naim app is just so slow. The artwork firms i 2 or 3 stages like dial up internet used to be.
The slowness in artwork rendering that you describe is definitely a network issue not the app and your 272 should stay connected all the time (like mine does for example).
You can take the advice or not, as you choose, but if it were me then I would be changing that router. They cost very little. I probably would change the switch at the same time too, as they cost very little too.