First, old version of Moodle. Somewhere around 2.7.x there were some fixes for files in Moodle - promised no more data loss (If I re-call, had to do with loosing files in filedir). If you have a bug there, no fixes forth coming.
If student was removed from the course or that account no longer exist, then that might explain ... but ...
/filedir/75/8e/8001188526048445b80af464c1079577
means that file (8001188526048445b80af464c1079577) should be in moodledata/filedir/75/8e/ is it?
Also strange ... usually Moodle uses the /75/8e/ directories as the first 4 characters in any file in 8e.
The meta data shows 8001.....
Normally, that would be 758e188526048445b80af464c1079577 ... so something is messed up either in the metadata mdl_files or the actual files themselves.
What's in moodledata/filedir/80/01/ ?
What's in moodledata/filedir/75/8e/ ?
If you could install moosh, it has a command that seeks out orphaned files ... as well as one that shows the metadata in mdl_files is messed up ... no correponding file physicially in filedir/XX/XX/whatever.
What to do to fix it? You might not be able to. :\
'spirit of sharing', Ken