I'm currently unable to stream HD FTA (free to air) channels without experiencing drop outs/freezing (SD quality works just fine...) using the Channels App on my FireTV 4K stick, I'm located in Australia.
These are the wireless values for my FireTV 4K stick which I pulled from the UniFi Network dashboard, so I don't believe it to be a wireless issue...
Channel 52 (11ac)
Signal 74% (-61 dBm)
Rx Rate 104 Mbps
Tx Rate 173 Mbps
Any help would be greatly appreciated!