If you are experiencing blank regions with now audio - then the problem might have to do with iCloud.
iCloud is clever about synchronizing your files - so as not to take up to much disk space.
The problem is, that it does not always download the files that you actually need.
What to do?
Open the File Folder associated with your session file.
In the Folder, you will see all your audio files.
If there is a Cloud icon next to the file - then Press the Cloud to download the file.
Make sure all the files are downloaded - and then try and open the session again.
The iCloud setting is called "Optimize Mac Storage"
You can find this in your Mac Settings / iCloud / iCloud Drive / Options
This is what is preventing all files from being downloaded.