At intervals (8)
'at intervals' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for every so often that I've seen before include "At intervals" , "Occasionally" .)
(Other definitions for episodic that I've seen before include "Occurring irregularly or in instalments" , "taken one piece at a time" , "Discursive" , "piecemeal" , "Intermittent" .)