So it seems like HP set the date to 13th of September in their firmware, when the printers should block non-HP cartridges. (Interesting part is, that they announced the acquisition of Samsung's printers division a day earlier)
HP Firmware Update - "Cartridges Missing or Damaged"
Which Printers Are Affected:
HP Officejet Pro 8610
HP Officejet Pro 8615
HP Officejet Pro 8620
HP Officejet Pro 8625
HP Officejet Pro 8630
HP Officejet Pro 8640
HP Officejet Pro 8660
HP Officejet Pro x576dw
HP Officejet Pro x476dw
HP Officejet Pro x476dn
HP Officejet Pro x551dw
HP Officejet Pro x451dw
HP Officejet Pro x451dn
HP Officejet 6830