Zwift soft-lock after 30-40 minutes of runtime

This is an odd issue. Here are the main details:

Intel NUC8i5BEH
OWC Helios FX GPU enclosure (TB3)
XFX AMD RX580 8GB
Windows 10

Zwift will run for hours without an issue using the integrated Iris video chipset, or with a crappy low power Nvidia based GPU. However, if I use the AMD it’ll soft-lock after about 35-40 minutes, where I have to alt-tab out of the game and come back to the game for it to continue rendering. It appears to be a hard freeze, but it’s not, for some reason the system just stops rendering. Once I alt-tab out and back in, the game will run for hours without having the same issue again.

I’m running the latest version of all the drivers, os, firmware, etc. I’m also running the latest version of Zwift (and it’s worth noting that I’ve always had this problem with this particular GPU and Zwift). I can run burn-in software like furmark for hours without issue though and I’ve played various other games as well.

Any idea? I have a GTX 1660 on it’s way, but I’m not in the habit of spending $300 if I don’t have to, and this XFX card is way past it’s return date, so if possible I’d like to get it working right.