MG2 in Mac OSX High SIerra is not scanning 3rd party plugins

It used to work and it actually scanned all my plugins some time ago, but now I am not able to make it scan them again. Also I am not even able to bring the 3rd party plugin into MG2 standalone despite the fact that they were on the scanning window. I erased everything , re-installed and the same issue. Any ideas? Thank you