Thank you for the image. After you switch the ink, is the nozzle check clean and full?
If the nozzle check is clean, then it is likely a buildup of ink around the outside edges of the printhead that the wiperblades are not able to reach. It looks as though the buildup of ink is much like a large 'drop' and the first pass of the printhead across the media makes contact.
If the nozzle check is not clean, and has gaps.... or if the ink mark is showing up in the middle of the nozzle check, it could be a damaged wiper blade, or a damaged seal on the pump cap assembly. It's not wiping off the excess ink on the MK/PK channel, and therefore causing a buildup on the printhead.
I would take a look at the wiper blade for PK/MK see if it is out of position, damaged, or has excess ink buildup.
Also, use a flashlight and check around the bottom of the printhead and around the capping station assembly. This could be an indication of a leaking seal in the tubes or somewhere at the connections and causing a small amount of ink to buildup on the bottom corners of the head. So take look around for drops of ink, small "spray" drops, or any ink that is not where it should be.
Next time you switch MK/PK, try running a power clean right after the procedure, then nozzle check. The power clean should attempt to wipe off the excess ink from the printhead if it is not damaged.
Lastly, the paper media looks like it's curling a little, and the highest poing of the curl is right around the ink mark. If the head is set to "narrow gap" in the media settings, and you're using thick media... it could cause ink marks, but it moreso looks like scratches and dashes on the media, and not as clean as the image you posted... so while the media does seem to curl in the image, it doesn't seem to be the problem here.
Since the printer is relatively new, you should be under warranty?
Hope it helps,