I just set up a new 5700 XT in a Razor Core X Enclosure and I'm not able to use Prorender with it at all. It Crashes shortly after launch. Sometimes, I'm able to navigate with viewport render (which is nice and fast), and then it goes down. I'm never able to use it for more than 1 minute. I have the external 5700 set up as the only render hardware. I've tried other combinations and there wasn't a change. I tried the latest 2.8.x and the Prorender beta with similar or even worse results.
I've tried loopback with the internal displace and only though the GPU with my monitor connected to the card directly.
There are no issues with the internal GPU (5500m) in either Mac or Windows. I'm not able to get my egpu working in Windows, so I can't test there.
Here's the MacOS error log from the last crash a few minutes ago blender-prorender-egpu-crash.txt · GitHub