Well currently, COVID-19 has created a challenge completing background checks as courts were not deemed essential businesses when everything shut down. Some states have reopened their courts with strict safety guidelines, but I imagine there is a backlog of work, fewer staff present, and if there is a COVID-19 exposure then the court may be closed again. So current interns pending background checks may be getting reports that the check can't be run due to court closures.
If you're referring to background check issues in years prior then sites that require them likely have criteria of what type of background is or is not acceptable. I've heard failing to disclose something on one's background or DUI's have caused problems.
