Like badly-synced dialogue offstage? (6,3,6)
I believe the answer is:
behind the scenes
'offstage?' is the definition.
('behind the scenes' can be a synonym of 'offstage')
I don't understand the remainder of the clue.
(Other definitions for behind the scenes that I've seen before include "in the private sector" , "Where stage hands work" , "backstage" , "Playwright is" , "out of public view" .)