Brand new Mac Pro... 16 core 96gb w5700x blah blah... dam thing freezes daily. I just got it this week. Tried disabling sleep, to see how it helps... I assume it's related to the w5700?
I wanted to post my experiences in the hope this can help a person struggling with this in the future. Because I wasted days on it. So, I got a base-configuration Mac Pro a couple weeks ago. I really wanted the W5700X but I got a good deal on the base config, to the point where I didn't lose any money to just order the W5700X from Apple at $1000 instead of the $600 it costs to include it in a custom build.
Anyway, the card came (from China, and impressively quickly, thanks UPS), I installed it, and of course the first thing I did was go to About This Mac to see what card it said I had installed now. Machine locked up immediately. This was repeatable. I contacted Apple, who couldn't figure it out (didn't try very hard to be honest), and just told me to send the card back and order another one. I had hoped that they'd next-day me one from their stock, but no.
So the second card came, from China, even more impressively quickly than the first one. (Shipped from Shanghai on June 17, and was delivered to me, in rural western North Carolina, TWO DAYS LATER, on June 19. All for $8. The day it was delivered it started out in Alaska. I thought there was no chance for a delivery but I was wrong. I digress...)
Second card did EXACTLY the same thing. I was convinced that the computer must be defective. But then, in a moment of inspiration, I decided to hook up the screen differently. I had been hooking it via a DisplayPort to USB-C cable to the "built-in" Thunderbolt ports at the top of the computer. I tried using HDMI to the port on the W5700X and no lock up! Now, this is an older 4K screen, and the HDMI on it does not support 60Hz (only 30), so I would not want to run it like that, but still, it worked! Then I tried it by DisplayPort to one of the Thunderbolt ports on the W5700X and it also worked, at 30Hz. But only two ports on the card worked... the other two displayed only the boot screen but no desktop. I hooked back up to an upper port to make sure that the problem hadn't somehow resolved, and it still locked up. Also, I forgot to say earlier, when I would leave the Mac running for a while (obviously without clicking the things that made it lock up), it would eventually lock up on its own anyway. Also, running System Information and clicking Graphics/Displays would cause a lockup every time.
The screen which was, apparently, causing the lockups was a Dell UP2414Q, an old (2014) 4K screen. More on this later.
Inspired, I tried a different screen. This time, an HP 5K screen model Z27Q, needing two DisplayPort to USB-C cables. This screen worked perfectly, at 60Hz, no lockups, no matter where it was connected! I was so upset because that was the screen I was going to really use with the computer anyway. I was only using the Dell for testing. I also left the computer running with the HP screen overnight and it never locked up.
Finally, I tried a newer Dell 4K screen, a P2415Q. This also worked perfectly no matter where connected.
I should add that for a long time I suspected Thunderbolt firmware to be the issue. I thought what was on the W5700X was older than what the computer had. Turns out I was reading the System Information screen wrong... bus 0 and 1 are on the card (as someone in this thread stated) and 2 and 3 are the upper built-in ports. My W5700X ports have 55.2 and the built-in ports have 49.4. The firmware for the built-in ports never updated, despite me clean reinstalling macOS, applying combo updates, and zapping NVRAM. It seems to me that 49.4 is the correct, current version and that's that. QUESTION: Does anyone have any higher version running for bus 2 or 3?
Anyway, the moral of the story: Somehow, the Dell UP2414Q had the power to lock up my computer when using the W5700X and connecting via DisplayPort to upper Thunderbolt ports (it did not happen with the original 580X installed, running from the same upper ports). My theory is that it has to do with the fact that this screen is an early 4K screen, using a technology called MST (multi-stream transport), instead of the newer ones which use SST (single-stream transport). That may have nothing to do with it; maybe it is just this particular model or even my particular copy of the model. To truly test the theory I'd need to connect a wide range of MST and SST screens to test, and I don't have a wide range of those screens.
As I said, I hope this helps someone. Likely, the combination of a modern Mac Pro running with a crusty old screen is an uncommon configuration, which would explain why my Google searches yielded nothing.