The ATV app is more device-resource intensive than most other apps (and less efficient with them), as well as using higher-than-average bitrates and more susceptible to changing network conditions (dropped frames/resolution/dropouts/de-sync).
You are also using an older slower less-capable 5+ year-old model (4630).
Things to try:
1) Change audio to STEREO: Settings/Audio/Digital output format=Stereo
2) Manually configure display to 1080p/720p: Settings/Display type=1080p/720p
3) Enable/disable refresh matching: Settings/System/Advanced system settings/Advanced display settings/Auto adjust display refresh rate = disabled/enabled
4) Switch to 5Ghz WiFi (if your 2.4+5Ghz SSIDs arent separated, you'll need to separate them)
5) Use ethernet instead of WiFi (less susceptible to network issues that cause de-sync/dropouts/etc)
6) Try a different/new HDMI cable (audio dropouts are common with older/"gone bad" cables)
7) Buy a new Roku - Express 4K+ (3941), Streaming Stick 4K (3820) are inexpensive ($25-50, currently $40) -if you want/need wired ethernet, get the Ultra/Ultra LT (or a USB ethernet adapter for the Express 4K+).
😎 Buy a competitor's device - FS4K/M, TS4K, O4KSB, GCCWTV are all obtainable for $20-50