Great question: it used to work wonderfully on my 4,1/5,1 Mac Pro, but after my house lost power briefly last week that machine started showing those symptoms. A few days ago I bought a few 5,1s from a local business and, after updating the BootROM to the latest (144.....) via Mojave, I swapped the CPU and RAM to what I had in the 4,1/5,1 cMP, put in the HDD with OCLP and my NVMEs containing Monterey and Win10 and still have those symptoms. The 4,1/5,1 stopped booting entirely after awhile, but now it boots again although it shows worse symptoms: Win10 video cuts out with each heavy demand on the GPU (tested with games and movies.) The 5,1 shows nothing on the MacOS side, though Win10 appears to run without issues.
For those who've noticed my other recent post, my two 4,1/5,1 Mac Pros appear to be damaged by a suspected power surge, and a 5,1 appears to be damaged by a power strip compromised by that surge (the cMP worked at first, then stopped doing anything at all soon after updating its BootROM. BootROM update was successful and it booted to Mojave, then died.) Replaced the power strip with a new UPS.
I have replaced the Sapphire with a XFX 580 and get the same behavior. I had a pixlas mod on both machines, but I think the connectors may be loose as I swapped that cable and connectors to the new PSU. I am now using a dual mini-6 pin to 8 pin connector and still get those behaviors, those less often. Using a Mac 5770 shows no negative behaviors.
I think tsialex suggested in another post on this site that a bad vid card can wreck a backplane? Perhaps my Sapphire, which was in the 4,1/5,1 during the power outage, was compromised and has now damaged one or more of the the 5,1 Mac Pros I bought recently?
I have swapped the CPU tray in the 5,1 and got the same behavior. I have swapped the RAM, too. Interestingly, when I boot to High Sierra on an old HDD I get no behaviors. Could this be pointing to a failing EVO Plus NVME?
Thanks for your time, everyone.
