Exporting into PDF/X4 and X3 doesn’t work with one old Mac Type 1 URW font (some other older Type 1 fonts do the same –but never TT or OT). And only that specific “Regular” typeface, all other work seamlessly. What’s interessting: All other Affinity Publisher PDF Export Settings work without problems. Also the path-conversion works for every fonts on this page. And guess what: Exporting PDF/X4 or 3 also works, if all fonts get converted to paths while exporting.
Samples in DMG for downloading in my dropbox https://www.dropbox.com/s/cknfynnxy6mstjr/20_07_18_Publisher-PDFX-export-issue.dmg?dl=0
best, Marcus