I had similar frustrating experience.
Tried to book with GGU's. Search would not show GGU option in filter box. Had to click "change search" a couple of time to get upgradable First fare to show up.
Selected First Upgradeable Fare (which showed F upgrade available ). After completion of booking, NO Option to add GGU's to booking.
Immediately cancelled booking.
Went back to search and selected Calendar with GGU applied. At that point, saw "you are looking at Classic Booking" .
FINALLY, familiar screen with solid blue for upgradable fares.
When selecting the fare, did receive notice that GGU can be applied to this booking upon completion. Long process for what was much easier.
Still have not received cancelled fare back to Wallet. 4 days and counting....