Hello.
I have tried several providers and applications (smart iptv, perfect player, kodi, live channels...etc), but I am experiencing buffering, stuttering and looping when using iptv with my Shield TV.
I have a wired 100/100 connection and I have absolutely no problems with Netflix, Youtube...etc. However, when I watch iptv through the same device it's choppy and not as smooth as I would like it to be. I am not in the UK or any other country where my ISP would block the traffic, so I know that's not the source of my problems.
Surely not all iptv providers are having problems at the same time, so I am thinking... is it the Shield? Any experiences?
I know you said you know it's not your ISP, but are you sure it's not your ISP?
The ability to stream everything flawlessly except IPTV really does lean toward it being ISP related. You could try a VPN to know for sure.