The solution is to not use the cloud for your files(other than as a backup method). Create "sessions" instead of "projects"(sessions live on your hard drive while projects are usually stored in the cloud). Then share in one of a few ways such as:
1-zip and send the full session using dropbox, wetransfer.com or a similar file sharing option.
2-bounce and email an MP3 file to your collaborator so they can add parts, and send those parts back as in option 1
I have used both these options with no issues, but for option 2, make sure you do a couple of things; bounce from zero on the timeline and make sure all participants know and use the same tempo(BPM). Any tracks that are shared should also be consolidated back to zero, OR, send stripped sessions that only include the new parts(so the person compiling everything can simply Import Session Data to bring the new parts into a "master" session)
