Puzzle being difficult (7)
I believe the answer is:
problem
I believe this clue is a double definition.
'puzzle' is the first definition.
(I've seen this before)
'difficult' is the second definition.
(thesaurus)
'being' is the link.
(Other definitions for problem that I've seen before include "Difficulty, poser" , "Quandary or dilemma" , "Question or source of perplexity" , "Difficult matter to solve" , "State of difficulty that needs to be resolved" .)