what is the issue on m8s? cause i'm targeting that one as well. 

can u describe a bit more...

.. "dwnload, upload speed" - how did u determine that for the box?
.. do u get same 3mbps dwnld instead of 30mbps with other devices on wifi?
.. what router r u using? orig unifi one?
.. yr house... double, single, 3 storey? how far box from router?

Your router is good.

Other devices receiving good.

The problem is box or app specific. What is this HDTV app?

If u use YouTube or some other app, what is the result?

so there will be no problem if we are using LAN cable?

I do not know this particular ahem iptv.

Video streaming smoothness is dependent on country geoblocks, site integrity, traffic volume, local authority throttling and yr equipment set up. One of them goes bad, u get poor reception.

I am now quite sure there is nothing wrong with your box or unifi. It is the ahem IPTV app not working well Since it is illegit, no guarantee. Aztro or any legit IPTV is not going to let hackers run wild for long.

Meanwhile, get a couple of common popular apps and try them. They should work good. Some apps are suggested in this thread, u can also Google to find them.

I have used many apps but over time, I come to use only a few reliable free ones since the rest are problematic. Problematic not becos of box or unifi but these apps are either not maintained well or get blocked very quickly.

if u can get that iptv working well on another device, then here is something not right about the box - could be memory problem, corrupted firmware/sys files... or hardware malfunction?

how old is the box?

U just bought it no? Have u checked with the seller? Maybe bring it to seller place to test or even test another unit?
Never heard this particular iptv provider before..could it be incompatible?