At irregular intervals (8)
'at irregular intervals' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for intermittently that I've seen before include "Not all the time" , "(Happening) with pauses now and then" , "sometimes" , "So as to occur at irregular intervals" .)
(Other definitions for sporadic that I've seen before include "Occasional - intermittent" , "Happening irregularly" , "Scattered - irregular" , "Picadors being scattered, here and there" , "infrequent" .)