Question about Sonnet eGFX Breakaway Box 550

The list of supported graphics cards can be found here https://support.apple.com/en-us... Just because the card has the same name doesn't mean it will work. It must be from AMD so that you don't have problems with High Sierra. Additionally, make sure you have the latest High Sierra version installed. If so, it is probably due to the "wrong" graphics card. Unfortunately, the effective cards from AMD are difficult to obtain in Switzerland. I had to resort to the competition from Digitec. You may find more information on the net.

If the topic is still topical and you still need help, take a look at https://egpu.io/. There you will find all the guides and troubleshootings as well as builds and experience reports.

The compatibility list <-- stupid word, of the Sonnet device is not to be understood in such a way that all cards on it also harmonise with Mac.... This list is only there to show which cards work in the Sonnet device in terms of power and size.

The list from Apple shows that the AMD cards work accordingly, this refers to all AMD cards, not only those from AMD itself but also the MSI Armor RX 580 because it also has an AMD chip on it. Your problem is clearly due to software problems, a defective Sonnet or a defective card, but not due to the basic harmonisation of the three devices. I know that doesn't really narrow down the source of the problem, but at least you know that it should theoretically work :)

A faulty graphics card does not normally crash a Mac/Pc. I assume it is HighSierra?
If possible, 1. test on another Mac and/or 2. with another graphics card. I know, both not exactly super tips... ;-)