I’ve used the bitmap fill feature for a long time in previous releases but when I downloaded the 18.104.22.1681 release it glitched on me. I think they’re something I’m missing. The left image is what I am seeing in AD before exporting to PDF. The right image is what I’m getting when saving to PDF which clearly shows only the one original bitmap fill is in the rectangle and tiling didn't transfer. I’ll also attach a screenshot of AD so you can see some settings.
Affinity Designer bitmap tiling not saving to PDF.pdf