I've had the same problem for the last few days. The sound works on the YouTube app if I switch to the TV speakers but not if I try to use my Roku Speakers. The Roku Speakers work fine for all the other apps I've tried, only having the problem with the YouTube app.
I am having the same issue as well and have gone through some troubleshooting steps. I uninstalled YT and then checked for a software update on the TV. Powered it off and on, reinstalled YT and issue has not been resolved. All other apps work fine so it is only the YT app that is having this issue. Sound from TV is fine when playing YT videos, but when used with Roku wireless speakers, the issue persists.
I contacted support through twitter and they offered some troubleshooting tips, but they were the same ones I had tried previously. I guess we have to wait for the YT app to be updated or the Roku software to be updated for their speakers.
I have the same problem exactly.. Roku refuses help.. Speakers are 9 months old. I notice it bad on You Tube 4k videos.. such as Costa Rica and Peru.. also the movie short of Sniper with Will Smith.. and others.. It only is a problem with using my Roku Wireless speakers.. (tv is TCL 55R625) If I use the TV built in speakers the audio is ok.. This just started in last few days as we were showing some friends the TCL and the wireless speakers a week a go and it was fine.
This is more of an issue with the YT app as it was recently updated last week that is causing these audio issues. We just have to wait for the app to be updated and see what happens. Once it is updated and the issue persists, then it is up to Roku to update their software on the TV or their speakers. It unfortunate since I use YT a lot and prefer having a minimal set up, but I’ve had my AppleTV connected to the TV and just using that for now until there is an update for YT or Roku speakers.