Hey Guys,
OK so I just had this issue for me I managed to get it resolved, it might not work for you but you can give it a try.
So the mouse was working fine for a few days and then this after noon I noticed a windows update was waiting to be installed [Win10 Pro 64bit], so I restarted my pc and let the windows update install, after I notice that non of my side buttons were working any more, everything else was fine but nothing from the side.
Here's some of the things I tried:
-Remap Key
-New CUE Profile
-Different USB Port
-Uninstalled Mouse via Device Manager
-Different Windows User Profile
In the end it appears that running a "Repair" on the CUE software is what has gotten it to work again for me, so I would recommend giving that ago.