Access 2608 Build 20326: Line controls disappear in Print Preview

This looks like a rendering regression in the Access build rather than a report design issue, especially since you reproduced it in a new MDB and with Microsoft Print to PDF. I would keep one tiny sample database with only the report, one Line control, and one Rectangle control, then attach screenshots from Design View and Print Preview when reporting it. For production reports, the practical workaround is to replace critical Line controls with very thin Rectangle controls until the fixed Current Channel Preview build reaches your channel. I would also test ACCDB and MDB separately, because that helps Microsoft confirm whether the problem is tied to the old file format or the report renderer itself.