Hello,
I experience a problem like this. To me, it seems Affinity Photo has problems with the translation from Adobe RGB to the printer ICC.
I have edited a picture in Affinity and created with the brush an outer ring of black & white. When I printed it with Affinity Photo it got an purple ring in the middle. After that I exported the file to sRGB jpg and printed it with Nikon Capture NX-D, which resulted in a print I actually saw on the screen.
I use an Epson Surecolor P600 printer.
Running Window 10 64bit
Using an AMD GPU R7 370
These pictures are taken with an Nikon D750, using Raw in AdobeRGB
I used On1 Raw 2020 for Raw conversion. Opened it via .PSD in Affinity and saved in Affinity-file-format
With kind regards,
Jaap Kloppenburg