Me thinks you've met your course from he--!
Had one of those for a couple of years. That one course (a multimedia course) killed automated backups .. never completed - via any method but command line. And had to resort to backing it up on a weekend cron job that backed up just that course! Grrrrr!
Look in moodledata/temp/backup/ssweajdfasjsfjasfjasdfl - one of those directories left from a failed restore. In there should be a moodle_backup.log ... if that file has any size - that will show the stage at which that restore failed.
It won't tell you how to solve the issue ... just info.
Don't know how much trouble it would for you to install moosh, but give it a try. It's command line only. Has a command for course info. Point that course info command to the course ID number that you cannot restore for some clues.
Here's an example of my course from he--! :
593 69 Honors Digital Media - Mr. Thomas DIM 1
Course ID: 593
No of contexts: 80
Context by level:
CONTEXT_MODULE (70): 76
CONTEXT_BLOCK (80): 4
Context by module:
assign (1): 55
forum (9): 1
resource (17): 17
url (20): 3
Number of role capability overwrites: 0
Role capability overwrites by context:
Number of local role assignments: 0
Locally assigned roles by context:
Number of enrolled users: 2
Users enrolled by role:
manager (1): 2
Number of groups: 0
Group statistics:
Min number of members in a group: 0
Max number of members in a group: 0
Avg number of members in a group: 0
Course modinfo size: 156839
Number of sections: 11
Section statistics:
Sections visible: 9
Sections hidden: 2
Min number of modules in a section: 0
Max number of modules in a section: 55
Avg number of modules in a section: 6
Number of grades: 0
Number of log entries: 0
Number of files: 8111
Total file size: 728186775
Cache build time: 0.024131059646606
The course is better managed now by teacher. The bold above used to show 13x GIG!
Best of luck!
'SoS', Ken