Hi Sean,
I don't have an eGPU, I'm using a 2017 Dell XPS 15 with the following specifications:
Intel Core i7 7700HQ 2.80Ghz with Intel HD Graphics 630
Nvidia GeForce GTX 1050
16 GB of RAM (DDR4 2400MHz)
The devices connected are the following:
2 external HDDs (USB-A connectors)
2 external displays (one connected on the HDMI port of the laptop and the other is connected through a USB-C to HDMI/USB/Ethernet/SD card adapter)
The Nvidia control panel says that Affinity Designer is using the integrated Intel graphics (auto selected by the Windows global settings). Forcing it to use the GTX 1050 doesn't change anything.
The configuration and the externals devices were already used before and there was no issue. It's the first time that I'm getting this and the only thing that changed is that the 2004 Windows 10 feature update got installed and I also installed the latest BIOS update from Dell (version 1.19.2 released on June 19th 2020).
I only have an Affinity Photo license for macOS so I can't tell you if the same problem would happen with Affinity Photo on my XPS.