Noticed that my TV updated to 9.2.0 build 4111-30 late last night and now my volume controls are extremely slow. When I click on volume up/down or mute, it take a few seconds for the TV to acknowledge. Same issue with using the Roku app on an Android phone. I even re-paired my remote to the TV. I'm assuming the latest update broke the volume control. I can see the white LED light flicker with each click but doesn't respond every time. TV is not connected to any other speakers or receivers. Anyone ever experience this? Do I have to wait for another update to fix this?
Try using the option in Settings>System>Power>System restart to restart your TV and see if this helps. I would also recommend unplugging your wireless router/modem for a few minutes to fully reboot them.
Once the router/modem are back online, check your TV's network connection once more to confirm it is connected (for mobile app control ability), then try adjusting the volume again.