I am using a replacement Roku Voice Remote Pro. It is a replacement sent to me after my last one started doing crazy things. Now this one is acting weird. Suddenly when I push the volume buttons on the remote, it will turn the volume all the way up or down. That is with one short click, not holding the button down. It's very annoying when you are trying to quietly watch TV and suddenly it's full blast.
I would suspect a sticking button. Unless you're using CEC (which if you don't know what it is you're not using it), the remote sends the volume commands via IR. The next time it happens take out your phone and point the remote at the phone's camera. If you can see a light on the end of the remote on your phone's screen then the button is sticking. My other guess would be some kind of interference from sunlight on the front of the TV or another remote with a stuck button.
This started happening to us this week as well, with two different remotes on two different Roku Ultras, so I know it’s not a hardware failure like a button sticking. And this was after Roku replaced both remotes a few months ago when they kept losing the ability to control my TV’s. I like the Roku product overall, but the ongoing issues with the remotes is forcing me to look at alternatives.
It seems in my case that the buttons are sticking internally somehow. The mechanical function isn't sticking, but if I interrupt the IR signal by putting something solid in front of it, it will stop the action until I move the solid. The only way to stop the up or down of the volume is to push the different direction. So it's definitely somehow sticking inside and giving a signal. Frustrating as this is also a replaced remote from another one with erratic behavior.