I'm having the same problem. The default profile is my only profile set up, and it remains active. My RGB lighting scheme continues to work properly, so my profile is loaded; and the side buttons (as well as the two center buttons below the wheel) simply stop responding.
The buttons are programmed to act as the keyboard's ten-key inputs, so I can test it by opening notepad and trying to type some numbers in. It does not work. After I restart the system, it begins to work again, and I may not have the problem again for several days.
The issue appears to strike at random, which is a shame because I adore the feel and ergonomics of this mouse. I sincerely hope a fix is coming soon! 2016-01-27T17-36-06.log.txt