Some users (inc me) have experienced problems with backing up Sampler Tracks.
Thanks to user Shazee, at least we can backup projects so Sampler Tracks get backed up correctly on Mac (im on Catalina).
The solution is NOT to use Minimize Audio during backup.
Using Minimize Audio renders Sampler Track content unusable, it will produce silence on my Macbook.
So if you untick Minimize Audio Files during backup File/Back up Project…) the Sample Track(s) work.
If i minimize audio by cleaning up the Pool before backup, its basically the same.