Where are AirDrop temp files located?
I guess it'd be quite outdated answer, but maybe it will save some time for others

AirDrop temp files hidden under this path /private/var/folders/, you need to look for folder called exactly like this "(A Document Being Saved By sharingd)" in subfolders. 

In my case it was /private/var/folders/fq/51d9_5dn7hg445wwp5n7kyqm0000gn/T/TemporaryItems/(A Document Being Saved By sharingd)