Are you sure that there is nothing else locking the drive? Something like
LockHunter can help identify this.
Additionally, if I'm remembering rigjt Windows itself can put a lock on the external drives - there's a setting where you can pick
'quick removal' or 'performance' and this can affect it.
EDIT: Googling is 'helpful' as ever (I entered 'file lock' and got results for 'password protect') but see this:
https://superuser.com/questions/1239...rnal-hard-disk