The first thing to do is to switch from PK to MK and do a cleaning and then check if there is a clog again. It could be an issue with your ink selector in the printer itself.
These printers have faulty design regarding channel dropout. A sudden drop-out of a full channel is not a nozzle clog that necessitates nozzle cleanings but is usually a more mechanical issue to do with either selector unit, print-head, or cleaning assembly on the printer itself that is forcing air back up into the print-head usually during a head clean or boot up of the printer.
Regarding the chip not reading on the 4900 cartridge, this can happen if the printer (or electricity system in the house) experiences any power surges or voltage jumps. The PK channel drop and faulty chip read could be related in fact. The chips are fragile and can also be disabled by static electricity.
I suggest anyone using refill carts get a backup set of chips just to be safe in their production and operation of the cartridges.