Have you tried recapturing other tapes (not from this shooter) today?
YES THEY ARE FINE
If other tapes are still capturing, obviously the problem lies with the tapes made by this shooter.
What gear did he use to down-convert and dub your copies?
HIS CANON XH-A1 AND A DSR-11
That would be where I’d suspect the problem lies.
(Especially if it was to another Canon camcorder.)
HE IS STUMPED TOO!