Searching on internet find this post today because i have the same problem but also i found the solution.
my printer is a Samsung M2026.
Until yesterday i print my PDF fine.
after a pop up window of my printer says this toner has print more pages from that is compatible start to print my invoices that have a PNG picture on it with black background or blur.
After many checks i notice one more problem.
my cartridge meshed up whit more toner than normally.
one more think is the red light that is for ink is on (not blinking).
the toner i use is aftermarket and i think and these toners they have some lock like originals.
so i change the cartridge with a new aftermarket and the problem solved!!!
Magic? I don't think so.
sorry for my English and i hope this post helps someone.