If you get this same drastic volume issue between 9 and 10 when using the RokuTV in Antenna/OTA mode, then I think more a hardware issue - manufacturer problem.
If this only occurs when using the Roku operating system (streaming channels/apps), then I would assume Roku issue. (whether or not can be corrected in a build update, another story).
Some of these issues get intertwined (like the OTA signal strength indicator issue a few months back affecting RokuTVs). Definitely a Roku OS issue, and eventually a Roku OS build update was released to fix it.
Just have to narrow down to where it actually occurs. My feeling though is that it probably is a hardware issue needing to be addressed by the manufacturer.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102