Hole in stocking a problem (3)
I believe the answer is:
gap
'hole' is the definition.
(thesaurus)
'in stocking a problem' is the wordplay.
'in' says the answer is hidden in the clue.
'GAP' is hidden within 'stocking a problem'.
(Other definitions for gap that I've seen before include "Break, hole, space" , "Pause" , "Aperture" , "Fissure" , "Breach or lacuna" .)