I've used the loop files that appear in the transfer window on a saved song and when I open the song again I get the locate missing files window! When I look for the loop files that were used on the songs I find that they're no longer in the studio one!
My Setup:
Mac Pro Retina
Mac OSX: Mojave 10.14.6 (18G2022)
Studio One 4.6
Presonus 192