Happen to be unoriginal (5)
I believe the answer is:
recur
'happen' is the definition.
(I know that recur is a more specific form of the action happen)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for recur that I've seen before include "come back to one's mind" , "Repeat" , "Be repeated" , "Return to mind" , "expected to return" .)