My Rival 600 has randomly stopped working ONLY on mousepads just today too, so I don't have the same issue as you, although I also suspect my issue is due to the firmware update as well.
not sure how to fix it. I hope if uninstall steel series software and reinstall the mouse without the drivers it will work good... kinda annoying, its happened with 2 mouses. Surprised others haven't complained. Aint the PC or the mouse, its the driver. Has to be.
But while i can use my rival 700 and works fine i really want the lighter mouse. I dont wanna have to say i bought a paperweight.... I hope it works raw drivers without the updated broken ass drivers from steel series.
I like steel series and before without other software never had a major problem. Have an arctis 7 and while they cant seem to fix this red light bug theres no other big major problems just the battery indicator is always red... but yet it still beeps when its low like it should. Have had SS keyboards also worked fine. And other mouses rival 300,700. Rival works flawless, just a big heavy.
Not sure why they have this problem with rival 600 drivers and IF IT WILL EVER BE FIXED.
Have you tried contacting Steelseries support? It's usually really good compared to most tech companies, they might have an answer.