When a member of a group fails to act consistently with a group norm, this is known as: ?

This is known as deviance.
Deviant behavior is a type of behavior that doesn't suit the rest of a group. So, if an individual acts differently than the rest of the society, he or she will be considered a deviant person. Deviant individuals are usually ostracized from the society due to their unacceptable behavior. 

Ongoing civil wars western roman empire finally collapsed476 c.e. romulus, the last of theroman  emperors in  the west, was overthrown by the germanic leader odoacer, who became the first barbarian to rule in rome. the order that the  roman empire  had brought towestern  europe for 1000 years was no more.