Sorry for not responding quicker, I was involved in workshops and trainings all last week, and was away from my computer.
Did the missing nozzles occur either shortly after installing a new or refilled refillable cartridge, or after the printer had sat unused for a while?
As Ken suggested, it may have been caused by air or debris, and to avoid too many cleaning cycles.
Please let me know if this reoccurs, you have further questions, or there's anything else I can help you with.
Best regards and happy printing~ Dana