Catalina problem with my Mac mini 2018 + Razer Core X enclosure + RX480 GPU
I can only comment about Mojave.
Can confirm a similar issue with Radeon RX 580 8 GB in Sonnet enclosure on the newest macOS Catalina 10.15.6 Beta (19G60d).
The filesystem is encrypted, so I can see the first prompt to enter my password and later it stuck on the boot picture.
Inspecting system logs didn't add much insight into what is the problem.
Heres the email I got from them
It's a year later, and I'm running version 10.15.7. But I'm having a similar problem: Mac mini 2018, Razer Core X Aluminum External GPU Enclosure, and XFX RX 5700 Xt Thicc III Ultra 8GB graphics card. With the monitor plugged into the graphics card, and the graphics card plugged into the Mac mini, sometimes it boots, and sometimes it doesn't. It's frustrating in the extreme to have just spent this much money only to have the whole thing be so unreliable.
I have two eGPUs:
I was never able, in a reliable way, to boot with the eGPU attached, whatever the OS version I used them with.
I will most probably submit a new feedback to Apple about this.
@psm, try this work around: leave the eGpu connected to the monitor and the Macmini to the eGpu (as you would for optimal performance) but at startup start with the Macmini and wait for 5 seconds before switching on the eGpu.
Hope this helps!