Spoke with Asus Technical Support. Once again an utter waste of time. His only advice was to reboot (duh...) and then check "My Computer" and see the volumes weren't there. When they didn't show up... his only advice was to pack up the entire 10lb computer and mail it off to some Asus support somewhere. If that's the best Asus can do for telephone tech support, I won't waste my time with them anymore.
UPDATE: Not sure which drive handles volumes E: and F: to be honest. I'll try pulling both drives and reseating them to see if that makes a difference. I'll also check the drive ribbon by pulling it and resetting it.
ANOTHER UPDATE: So I removed the ribbon cable and reseated it carefully. Looks like it might have been tugged a bit as it was a little exposed. Turned the computer back on, and both volumes are back...
SAD to think Asus Close Support would have had me send something back and do a 10 day turnaround for something this simple...
Asus Strix G733QSA-XS99-17.3-Inch Gaming Laptop
GeForce RTX 3080, AMD Ryzen 9 5900HX
360Hz 3ms 17.3” Full HD 1920x1080 IPS-Type Display
Razer Deathadder v2 Mouse
Verizon FiOS: Gigabit connection