Are you talking about when inserting an arXiv link to find similar papers? In that case, it is important that the paper being referenced is already stored in the database. If it's a very recent paper (as in less than a week or two old), it won't work. This should be easy to fix, though, by simply scraping the abstract from arxiv.org and using it as the query.

If you're talking about searching for specific papers, I'd be interested to know the queries and the desired result. Feel free to post it here or in a DM 🙂