Hmm thats odd. I have 2 STRIX 1080Ti OC cards in my SLI rig with no issues. Colors fade correctly in rainbow or music mode, etc. Are you running the latest version of Aura that was posted here?
EDIT: Here is a video I posted on Reddit showing the awesome party mode. You can see the cards flashing between red / orange and at the end they go off / on in time.