I found this related to nvml error
Anyway, I believe this particular error is related to connection between riser and the GPU it self. It might be faulty riser or simply not good connection. It could be triggered if you play with the GPU while working (slightly push it left right - definitely not recommended
Reattach all of your riser/GPU connections. Sometimes switching GPU places might help as well. Reboot. It may never repeat again. At least this is my impression for this error. @mares992 Your old cards might be just OK.
Is related to fan speed, if that make sense to you. good luck mate.