After a clean upgrade to Eagle 8.5.2 I couldn’t find the (new) managed libraries.
The user folder in “Documents” is fine with all the work and all the versions inside.
The answer seems to be that you have to re-import them and it makes some sense, but it would be better if it was some link to them in the Control Panel.
The fact that it is no auto-update is the best choice because you may have some file that wouldn’t need the updated library because you strangely placed something on the board.
The quick import procedure follows:
Open Library Manager > go to the Available panel > import by downloading all you need > check that all is fine in the In Use panel > close Library Manager.