When putting the eGPU under load the HD 520 crashes and recovers about every 30 minutes and when not putting the GPU under load it crashes about once a day.
I'm using the Dell XPS 13 with the 6200U and the 1080p display. I'm not sure on how to recreate this but it crashes mostly when playing besiege. It doesn't crash when running a stress test on XTU.
New drivers were developed to address this problem, I recommend updating to the latest video drivers. Below you will find driver version 4474:
Please test the driver linked above and if the problem remains, let me know about it.