Sorry to drag this thread back up from the dead but I have had this experience quite a lot and it's extremely frustrating, I have wasted so many nice bits of glossy card etc., it's genuinely getting quite expensive because you never know when it'll strike! (It is consistent with the same documents if re-tried though.)
I too have a Canon printer (iP8700 series), but I do not see this issue with anything other than Affinity.
Like the original poster above, I see lines appearing at the outer edges (crop boundary) of certain images when printed, which are not present on the design.
The only fix I have found is exporting the file as a PDF (uncompressed so I don't lose quality) and printing from that. Again, this appears to confirm that the problem is with Affinity's printing process itself, since I'm literally printing the same text and graphics to the same printer but from a PDF and they then come out fine.
Is there a way to formally raise this as a bug that needs resolving or is this forum that place?
Thanks very much,
Paul