Same issue here. I think I also have the WD TV Live 3rd Gen version. Did you find a resolution yet?
I don’t know what you mean by Youtube ‘leanback’ - I assume the App is the ‘YouTube for Android TV’.
If so, then I suspect it’s a compatibility issue since the latest version released on June 15th 2020 - https://play.google.com/store/apps/details?id=com.google.android.youtube.tv&hl=en_IE
So I think the question is - can we rollback to the previous version of Youtube?
The Google play store link above states that YouTube for Android TV requires Android 5.0 and above - but I have no idea which version of Android these WD TV Live 3rd Gen version are installed with.
Just to add, I tried rolling back to a few previous firmware’s (2.02.32, 2.01.86, 1.16.13) but I couldn’t even open Youtube with any of these.
The Youtube app version in the media player itself is web_20200624_00_rc00.
I assume that indicates the date of the update - 2020 06 24.
But I can’t see any option to roll this back.
Netflix is still working on it but maybe time to invest in a new product