Same issue as original post. Doesn't happen when i receive a call, only if I make one. As soon as I hang up, ringer volume is set back down very low.
Also noticed around the same time, I tried to uninstall Android system sweeper to clear cache, etc. Didn't use it, installed, uninstalled as I found a better one, but the the icon for the app won't go away. if I click on it, system tells me app no longer exists, and thus it also doesn't show up in my applications directory to uninstall. Maybe related?