I’m surprised that there isn’t an IJM response to this issue, but I assume there will be. I’ve had this exact problem on several desktop printers - both colour and Piezo. You can certainly print it out as suggested using flush images and calibration mode in QTR, but I predict that it will come back.
The IJM position is usually that this is caused by a dirty capping station or wiper blade or print head, and you need to do a clean. That’s certainly possible. If the problem still persists, then they say that it could be a faulty capping station and pump.
However on my Piezo R1900, I had this once, and given my precise symptoms I suspected two carts as being slow leakers. I replaced them and the problem went away, which I consider proved the point.
When you get this sort of cross-channel contamination a clean is a good idea. But it can be hard to know what the precise cause is, if the problem doesn’t go away after a cleaning routine. My view is that cartridge issues are more common that people realise, and IMHO it’s not a coincidence that IJM have just launched a completely new desktop cart design.