BIOS update F4g for Gigabyte Aorus Xtreme Waterforce 5G (Rev. 1) was issued on 2021-01-19. Upon flashing the BIOS, the Yamaha USB driver 2.0.4 would no longer recognize my AXR4 USB interface.
After having no luck tinkering with Windows settings, I rolled-back the BIOS to version F4f and all returned to normal operation.
Caution: The Gigabyte website no longer lists the F4f BIOS version, so save a copy of your current BIOS prior to any upgrade. (No hyperlinks can be included in forum posts.)
The issue has been reported to GIGABYTE and Steinberg. Perhaps a future Yamaha USB driver update will be compatible with F4g.
I wanted to log this known issue–as of 2021-01–for the benefit of other AXR4 users.