The suction is at maximum as is the head height. I've printed with these same papers for years and this has never happened so it has to be something independent of head height or suction.
Are you sure the suction is working properly? Is it holding the paper down in the platen area? If you've been doing this for years and are suddenly getting this I'm wondering what has suddenly changed or broken.
Is there a way to release the print head so I can move it to the center and check to see if there's a piece of debris under the head?
Do a 'change cutter blade' function to get at the carriage assembly.
I checked the Canon wiki website and there's nothing there... nor is there anything in the Canon manual.
The wiki is THE place to be for iPF stuff. This exact thing has been discussed over and over again in great detail. Give it another shot.
Also, when you place the cut sheet on a table, does it lie completely flat?