The ink will thicken up over time, and eventually this will affect the printing quality and electrical properties / solderability. This could very well be what you're seeing. Can you check the lot number of the conductive ink? It'll be written on the cartridge.
Another consequence of expired ink is that the seal in the piston may be broken due to the increased pressure required for dispensing. Check to see if there's ink in the cartridge barrel, behind the piston.
However, it could also be that some ink has dried out in the nozzle - I'd suggest trying to purge some ink manually for about 10s. You can also try cleaning out a nozzle if you don't have a spare to test out - see the recent comments in this thread.