Looks like a classic case of one cartridge, in this case one of the blacks, stopping totally. Even though
you have plenty of left.
I have never had it happen while in the middle of a print, but my 9880's did it mostly with cyan, or yellow.
You make one print fine, then next one is obviously wrong i.e. missing a color and when you do a NZ check,
one color is totally missing.
(3) different 9880's did this and finally the last one I received last year was OK.
When my 9880 did this you had to turn it off and then, pull the cart that was missing, and then most time
do 1 reg. clean. Since yours made the next print OK, then somehow it corrected it self. Do you have ANC
on? It sure should have caught the problem and run a cleaning cycle before the next print.
Paul Caldwell