Export to Pdf

Hi, one of our customers
sent me today report


black pictures should be transparent. This never happened
before, any idea whats wrong?
I can't reproduce the problem on my PC

pdf := TFlexCelPdfExport.Create(Xls, true);

OS on clients machine: Windows 10 64bit (10.0.18362)

I am not really sure in what can be happening here, but we use GDI+ to do the  image manipulation and convert the png in something the pdf can show.
So maybe something is wrong with GDI+ in his computer? Has he tried restarting the machine?  (I've seen very rarely GDI+ bugs that go away when you restart, probable related to too many GDI+ objects in use)

I can't really think on much more that could be causing this. If exporting as PDF/A1 you might see a similar problem, because PDF/A1 doesn't support transparency, but I assume this pdf is not a PDF/A1?

No its not and as I said, works everywhere
but on one PC :(

restart solved the problem.