Hi there - I've recently updated to 2.5.1 but having the same problem of my favourites disappearing every time I open/close a session.
I've tried implementing the process you've posted in a different thread but I don't even have the Arturia Library folder to change the preferences. In fact I can't even find it on my old system that was running 2.2.1. Where exactly do I find it - and if it can't be found (not there in the first place) - where can I download it?!
Do I need to to uninstall 2.5.1 and then reinstall it and change the preferences there or something?
REALLY frustrating as have spent long periods of time picking out sounds that I'd like to use for future projects and all gone within a split second!
I look forward to hearing from you on this...
Many thanks!