I'm having problems with my P3 and riser cable too.
First cable caused reboots, boots with no image, driver fails warnings, and constant latency spikes and sound stuttering.
Contacted Thermaltake, and got no response so far, not even a "Thank you for contacting us".
I'm from Portugal, and dealt with the store I bought the case from (PcComponentes, in Spain).
They sent me a new cable yesterday, which I assembled so very carefully avoiding cable strain and keep the cable curves as wide as possible.
First run on new cable: same constant latency spikes and sound stuttering.
GPU went b