Go in and clear cache and settings on Pluto. Reboot. If it does not work, uninstall Pluto, reboot and reinstall. Works fine on my 4k sticks.
As an aside: https://github.com/Free-IPTV/Countries
Legal free iptv source. Up to you to figure out how to use it, but there are hundreds of US channels including live OAN.
Stupid question but how do you clear cache on Pluto?