Image in a photo contest cannot be deleted by admin

An image in a photo contest which is visible to the user is shown as disapproved. The same image cannot be seen by the Admin for the PollUnit, thus it cannot be deleted so the user can enter another photo. The PollUnit name is 'Challenge #60 Overexposed/High Key'. The image name is '_1089159-fullframe'. Please delete this image and, if possible, explain how this could have happened.

Hi Steve,
I could not find the image in the contest.
Did you manage to delete it?
Kind regards
Philipp