It seems like that problem traces to the USB VID and PID that the u-boot USB gadget reports. We hadn't changed the default defconfig settings for "CONFIG_USB_GADGET_VENDOR_NUM" and "CONFIG_USB_GADGET_PRODUCT_NUM" from what they were in the distribution, and that seems to trace to a commit dating back to 2015. That commit sets the u-boot gadget VID to 0x0f25 which seems to be registered to "Netchip Technology, Inc", and PID to 0xA4A5 which would be a "Pocketbook Pro903" device.