1) When reinstalling an app, make sure you restart your Roku after removing & before reinstalling:
A) Remove App B) RESTART Roku (Must do this here!) C) Reinstall app
2) Apple tends to use higher bitrates than its competitors, so even though the signal is excellent, the speed may be an issue - use Settings/Network/Check Connection to test the speed, then check it ("Internet download speed") with Settings/Network/About.
3) Otherwise, if your speed is fine (~25-30Mbps or higher preferred), try:
A) Manually configure display: Settings/Display type = 1080p TV (do NOT use Auto) - try again
B) Change audio to stereo: Settings/Audio/Audio mode = Stereo, Settings/Audio/Digital output format = Stereo - try again
C) Enable/Disable refresh rate matching: Settings/System/Advanced system settings/Advanced display settings/Auto-adjust display refresh rate = On (or off if currently enabled) - try again