Like many of you, I have experienced the growing pains of transition to Fab.com. My entire library disappeared from the Epic Launcher, Fab UE Plugin was nowhere to be found, etc. I had the most recent version of the launcher and the engine installed and just could not get it to work.
What solved it for me was enabling game library for a moment. Unchecking the box next to Hide Game Library somehow “unplugged” the launcher and made it connect to Fab and pull the data.
I am sure this is a bug and not the intended behavior - but to all that still struggle, try it out!
Yes - this worked for me too (after wasting time trying other things), For other people looking for this, go to your account settings in Epic Games Launcher. Toggle Hide Game Library (you will get a warning). Then go back in and immediately un-check it again. I got a new yellow sync Fab icon. After clicking that, all my assets appeared in the vault. However, they still do NOT appear in the Fab plugin - which still shows MyLibrary as completely empty.