Relaxing set grin is problematic (7)
I believe the answer is:
'relaxing' is the definition.
(I've seen this before)
'set grin is problematic' is the wordplay.
'is problematic' indicates anagramming the letters.
'setgrin' anagrammed gives 'RESTING'.
(Other definitions for resting that I've seen before include "Taking a break" , "Lying down" , "(Of actors) currently unemployed" , "(Of actor) not working" , "not in a cast" .)