Hey there, thanks for posting your question, I actually had a similar situation (not sure if its the exact same situation) however, I bought a brand new roku ultra and replaced the roku express and the remote was still either getting stuck going way up on volume or way down when trying to bearly turn up or down the volume.
The roku remote volume works off of IR (infrared) that the regular TV remote uses. I found out that in order to replicate the situation it only happened when content was playing on the screen. If I was on the home screen it would not have the issue happen.
Now that I learned how the roku TV remote works and understood how to replicate the issue I was able to start playing around and finding a solution. The solution was actually 2 parts. The main thing was that I had both the roku express and the roku ultra mounted right in the center of my TV on the bottom of it via double sided removable sticky pad that Roku provides in the package. This was SUPER close to the IR blaster (next to it, and not on top of it by any means but literally right next to it). This for whatever reason made me discover that there was some sort of interference in the signal getting passed to the TV. I moved the Roku to be away from the IR blaster by mounting it on the opposide side of the TV and this fixed the issue for me. In addition, I cleaned the IR receiver on the TV and the Roku remote as the second step and just for good measure.
I hope this helps educate you on the workings of the Roku remote and how it controls the TV as well as best practices on where to mount the Roku to avoid this particular issue.
