warningFactur-X / ZUGFeRD containercontainerPDF
The PDF catalog must reference the embedded invoice in its /AF (Associated Files) array.
The PDF catalog has no /AF array, so the embedded invoice is not declared as an associated file of the document.
Add an /AF entry on the document catalog pointing at the file specification for factur-x.xml. Attaching only through the EmbeddedFiles name tree usually still works, but readers that follow the specification look at /AF first.