All my problems with my Roku Express 5.1 surround and Lip Syncing started after the 9.4 update this November 2020.
Its so bad if Roku fails to sort it then I'm ditching my Roku and buying another brand.
I have the AT&T app on roku and NBC is always way out of sync with audio. Other channels not bad but NBC was the worst. I went in to settings on the roku, under "display type", I changed it from 1080 to 720. Problem solved, audio is perfect.
Ok interesting what is the point then of using this to replace my ATTTv Box since it won't display at the higher resolutions... But at least it will let me know if it is something with the ATTTv app