Quick follow up:
IT'S FIXED! Here's how:
in Users\ *username * \appdata\roaming\fahclient directory, there is a file called GPUs.txt. This is the list of supported GPU's, and you can't have a GPU slot if your card isn't in it. Mine was, but was removed.
The 2070 RTX Super apparently has several variants, so I opened a thread on the F&H forum to have my card white listed. After a few hours, the admin let me know he added my card with the info I provided (mainly the device ID).
Then I closed my local F&H software, deleted this TXT file, and restarted F&H. This forced the updated txt file to download to my system. I could then add a GPU slot in Advanced Control in seconds.
There's no info on why my particular variant of the 2070 Super was removed, but it's back now, and my GPU is a furnace again. I'm up to a score of 89 million, whatever that means!