If anybody is curious I finally got an answer from Steelseries support (but it doesn't work)
It seems that Windows is the culprit here. When we issue a firmware update through SSE, we send a signal to the OS to put your device into bootloader mode. Windows 7, in particular, can have major issues with this step. Most of the time it will work perfectly, but there are instances when the OS has an issue. When the device goes into bootloader mode, it will always create a different PID, and Windows thinks there is now a new device installed. The OS tries to load a bunch of information for that PID, in the background, and will time out our firmware update.
To remedy this you can manually put your device into bootloader mode.
Rival 300:
1. Hold both of the side buttons + the CPI button simultaneously.
This will enter bootloader mode manually and allow you to update the firmware accordingly.
Rival 700:
1. Hold both Mouse4 and Mouse5 + the CPI button simultaneously.
This will enter bootloader mode manually and allow you to update the firmware accordingly.
Thank you for your patience with this! Have a great day!
Regards,
Russ B
SteelSeries Support