Heater Fan Failure

Hello All,
just replaced my blower fan motor assembly with nice used one from a8 parts.
Fan was very noisy but no codes in vag-com,then i stripped it out drivers side impeller damaged ?? (see attached pics) anyone seen this before / any idea as to cause of failure.Heater box not been apart for long time 2 x screw heads sheared off requiring repair & top mesh was installed ok







regards Adrian