There were some incidents back in version 5.33.x.x that were creating duplicate AP lines on Bills to Supplier accounts. This is very rare to happen if ever in the current release. This is because all the causes of this issue to date have been found and eliminated.
In order to fix this problem you go to the integrity checks > edit single transaction and remove the offending line.
Video source: faq:integrity_checks:example_edit_single_transaction_deleting_duplicate_gl_line384k.flv