Thanks for reporting this.
I have fixed the problem now by changing the Ghostscript call to count
pages in a PDF file.
See
https://github.com/OpenPrinting/cups-filters/commit/297cc2d
I found this solution with the help of a bug report to Arch Linux:
https://bugs.archlinux.org/task/62251
There they have found the alternative method and also talked with the
Ghostscript developers on IRC to confirm the need of the change.
The old call used the undocumented internal "pdfdict" of Ghostscript
which from Ghostscript 9.27 on is not accessible any more for security
reasons. Now I use the call suggested in the Arch Linux bug report using
"runpdfbegin".
Till
