I have been recently having this issue as well. Roku Ultra 4802X with Voice Remote, running on HDMI2 on LG tv model 43UQ8000AUB with their "Magic Remote". I'm not yet 100% certain, but I think I fixed the issue today after reading this thread.
Here are the many steps I did to fix this with no success: Roku software updates, pairing the remote, removing the Roku from the TV's settings and re-adding it, trying to change the sound settings from IR to CEC (CEC did not work on my tv), trying to update the TV's operating system (The LG operating system was already up-to-date.)
After reading this post, I followed the diagnostic instructions to try different tv codes. After going thru 7 different codes, only the 2nd code which has always been the code I've used worked to silence the test music playing.
This prompted me to dig deep in all the tv setting menus and find a setting that had linked the LG Remote as a "Universal Remote Control" function for the Roku. I deleted that profile so the LG remote no longer controls the Roku. Since I did this, I cannot duplicate the volume up and up and up issue.
If you have an LG tv, see if the LG remote is acting as a universal remote tied to the Roku. If so, delete the setting on the LG tv settings menu. If you have a different brand, I'd check to see if there is a universal remote control setting that works the way the LG does; if so, delete the setting and test the Roku remote to see if you fixed the problem.
