I did some more printing with the same chemistry and an older box of Fuji Crystal Archive paper which worked fine. So it looks like my latest purchase is a different paper.
I'm wondering why the box states it is suitable for digital and optical exposure? Is the optical exposure something other than RA4 printing?
Digital printers use colour lasers to produce an image on paper, optical exposure is through an enlarger. The one difference is that you may need a slightly different filter pack for the digital/optical paper, as the lasers have a slightly different colour balance.