Just to update:
After uninstalling both Pro Tools 12 and Pro Tools First and then reinstalling Pro Tools 12 the plugins are there! :)
My guess is that Pro Tools 12 doesn't overwrite some of Pro Tools First files and that was causing the plugins not to load. So I reckon it's always advisable to uninstall Pro Tools First before installing 12. xD
Anyway, thanks a lot for the help!
