Same problem here. Fresh install of 2.1.1+. Created a test course with one file. Restore worked as you said with no activities, tried with only the file activity and error. Tried with the forum activity and no error.
Looking at the first error "line 1062 of /lib/filestorate/file_pool_content_exception thrown" I assume it is a file structure problem.
As I need to copy over 75 courses, it would be extreemly time consuming to create each one from scratch, so I need to be able to restore as soon as possible.
Did you ever get a solution for this????
Any help would be appreciated.