Hello - please assist!

One very important document suddrenly disappeared. It is not a file that has a collaborator, nor can it be located in trash or any other (current) location. This exact document was available for on the mobile app for a split second then quickly disappeared from view. I have no idea what is going on, but the file is missing - and it was not due to me (or anyone else) deleting it. 

Please assist.

Thank you, Anita