Problem of Beethoven perhaps, sacking the first three (5)

I believe the answer is:

poser

I'm a little stuck... Click here to teach me more about this clue!

'problem' is the definition.
(poser is a kind of problem)

I don't understand the remainder of the clue.

(Other definitions for poser that I've seen before include "Pseud" , "Problem set by the model" , "Person still being portrayed" , "Puzzling question for the model" , "insincere?" .)

I've seen this clue in The Telegraph.

Want a hint initially instead of a full solution? Install my app