Roku Ultra, latest (Aug '24) software version.
After some random amount of time (sometimes as low as ten minutes, sometimes a couple hours or more) the volume output by my Roku Ultra will change suddenly. It usually goes to a distortedly loud level, but will occasionally go to about a third of the previous volume. The optimum way I have discovered to recover from this is to pause whatever I'm watching or playing, cycle power on the Roku and go back to whatever I was watching or playing. The volume is now normal again.
At no point do I ever touch the volume buttons on my Roku remote or my sound system remote. This is nothing to do with my HDMI cabling or TV inputs as the same happens when using headphones to listen.
This has become markedly more frequent over the last few weeks. It used to happen maybe once or twice a month and it now happens multiple times in a single evening.