I did find "lumpy demand" in English in a Dutch reference (not, however, in a German one), and since it does seem to be a terminus technicus that is explained as sporadic demand, it might not be a bad idea to leave the English term (either in the heading itself or else later on in the text). Synonyms for sporadisch are gelegentlich, verstreut, vereinzelt vorkommend [Duden], and you might be able to use one of those to avoid using sporadisch twice in a row.
Other possibilities might be "stoßweise" or "stoßweise auftretend".


HTH.