Air is getting into cartridge ink channels and ink lines

I recently was printing with 9600 with the piezo carbon inks and noticed some very small lines in a print. I did a nozzle test and found some blank nozzles in the magenta and light cyan (#4 & 5 cart positions) patterns. I looked at the ink lines and found large air bubbles in the line. Air was also in the cartridge ink channels. The cartridges are not low on ink so my only idea of where the air could be coming in is at the cartridge seal. Oh the air vents are not blocked. Any idea of how to stop air inflow?
Two months ago I was making prints with no problems.

I just took out carts and found some air in most of the cart ink channels, got those bubbles out and reinstalled carts.

Hi Robert~

After reviewing your order history, I see you bought refillable carts for your 9600 in 2013, and also a set in 2009, so I assume they’ve been working well for quite a while… I recommend tilting carts exit valve down and tapping the exit channel a few times to force air into the cartridge body, and fill the exit channels with ink, then reinstall carts, making sure to push them snugly into the printer before lowering the cartridge locking lever.

Please let me know if air returns after doing this, or if there’s anything else I can help you with.

Best regards~ Dana