I've been using ui16 for around the year now and apart from occasional hickup caused by my Android tablet haven't experienced many issues with it.
I mainly use it for studio and live band mixing with FOH, floor monitors on 2xAUX and IEM on 2xAUX>
Before I bought it I've read very useful comments about Wifi not being reliable, etc, etc.
Since I used external Wifi router anyway for quite some time it did not bother me (BTW, I use Behringer XR18 on occasions too, when I need to record band performance in multitrack session) so it was nothing new for me.
However, on one occasion in studio I've experimented with different antennas and have found out that major cause of problems with ui16 and built-in Wifi is actually poor quality antenna supplied with the unit.
With original antenna connectivity from Android Tablet was limited to 5-6 meters in an empty room.
With any other antenna I've tried (some looking just slightly different than OEM supplied) connectivity went to very reliable 15-30 meters in empty room and it stayed the same at live performances.
So my opinion is that OEM antenna included with unit is just bad.
I am using antenna that I took from NB604N modem and since I never had to use external router.
Hope this will helps.