That, and mixing reference details from multiple sources and messing it up.

Let's say you read a paper on Arxiv but cite the version that was submitted to a journal or conference, without realizing that the authors made changes to the version they submitted and forgot to upload them to Arxiv.

In physics, references which just didn't exist. That could be that the author made it up, but often it's because they transcribed the reference from another paper without reading it - we know because a few people have deliberately introduced fake references to trace how far they would go. The reasons are not the same as for AI, but the problem they produce is the same.

References which don't accurately reflect the quoted material seem more common in other subjects.