No line numbers in stack trace with portable PDBs

Any idea why I don't seem to get line numbers in my stack traces dumped from ExcelDna for libraries in the stack which use portable PDBs?

I'm using .Net Framework 4.7.2 which AFAICT should support portable PDBs properly. Temporarily switching from portable to full (which I can't do longer term) does cause line numbers to show up in Excel, so it seems specific to the PDB type rather than that it e.g. cannot find the PDB; however, dumping stack traces from the same libraries with portable PDB, but from other applications (i.e. not excel) correctly show the line numbers in the stack trace - so for some reason the problem is specific to Excel/ExcelDNA?

Related:
#204, #111

Thanks