In the default settings, if two papers have the same Doi and the user doesn't set the doc_id, they'll have the same dockey, leading to one paper unable to be found.

elif "doc_id" not in data or not data["doc_id"]: # keep user defined doc_ids data["doc_id"] = encode_id(uuid4()) if "dockey" in data.get( "fields_to_overwrite_from_metadata", DEFAULT_FIELDS_TO_OVERWRITE_FROM_METADATA, ) and ("dockey" not in data or not data["dockey"]): data["dockey"] = data["doc_id"]

It may happen on the circumstance of two papers having the same Doi (e.g. one paper is normal thesis, the other one is its supplement information, like those published on ACS)