yikes! that is random!
was expecting to see some sort of ink dropout, but looks like the printhead decides to fire all colors at once at random.
possibly a dirty encoder strip or a piece of lint/cathair on the encoder sensor?
else it could be an issue with one of the ribbon cables starting to fail, getting pinched in such a way that it causes a tiny short in the data being transmitted to the printhead during movement.
someone else had a similar issue
here in this thread