For anyone dealing with this issue on with an ARC sound system, I managed to fix this issue by doing the following:
1. Disable ARC so the TV is playing sound through TV speakers 2. Setup Remote using settings menu on Roku - Check that Roku remote can turn on/off and volume 3. Re-enable ARC to play through sound system- Roku should still turn on/off TV and volume control through ARC will work
Trying to setup the remote with the sound system engaged did work despite the system muting when prompted. I think the remote was picking up sound system IR instead of the TV IR. Silly to me that Roku didn't test compatibility with ARC systems prior to their updates.
I have a Roku Voice Remote RC399 which I purchased based on your suggestion that my volume sticking problem required a new remote. It's about 5 weeks old and the volume sticks and the power button is not great.
Software version 10.0.0 build 4195-AE
Samsung TV model #UN50MU6300FXZA
Come on Roku. You are not building any brand loyalty here.
Considering the other recent actions of these money grubbing cheese lords, it is probably intentional that they are deactivating the power and volume controls except on their approved brands of TV's.... sort of like what they did with all the apps they removed.
The latest update did not fix the volume and power control, however this whole thing is a bit confusing because our 2nd Roku located in a different room never lost either the volume nor the power control with a very similar Samsung TV