The November 14th firmware (3.13.1) update accidentally caused major issues for some Rival 600 users. SteelSeries immediately pulled the update and identified the problem.
Here's how to fix it if you were one of the unlucky few:
How to recover:
Unplug any SteelSeries devices from your computer.
Hold left click + right click + CPI button and plug in your Rival 600 while holding them down.
The SteelSeries logo on the Rival 600 should start blinking blue. If not, unplug the mouse and try step 2 again.
Run the _UPDATE_APPLICATION.bat file to recover the mouse.
https://support.steelseries.com/hc/en-us/articles/360019826691-Our-bad-with-the-whole-Rival-600-not-working-Rival-600-fix-