Deprovisioned user not deleting

so every now and then  i end up with a deprovisioned user not deleting 

the deletiondate has a value data set for when to delete, but it gets left behind in recycle bin, and i have to go and manually clean up

what other options/permissions should i check on the object

in the passed if domain admin didnt have full access, we would change this, but its often not the case and the object has domain admin set to full