Black and color error together but not separately

[PhilMC]

I have CL-641XL and PG-640XL cartridges that I'm trying to install in my Canon MG3600. When installing both at the same time, the alarm flashes four times which a quick google search has shown to be error code 1687 - FINE cartridge is not installed properly. When I install each cartridge separately, I don't receive an error.

It would be easy enough to purchase new cartridges, but now my curiosity has gotten the best of me.

Can anyone help explain why they wont install together? TIA