In a mass-production setting.

I'm not so happy with the previous two suggestions of "backlog" (which imo means "Rückstand") and "bottleneck" (I think of a bottleneck being a more permanent situation whereas my text means there has been a problem somewhere else in the machinery that has lead to a Teilerückstau.

I thought of "parts backup" but there aren't enough great Google hits to make me confident of that one. (On the other hand, "Teilerückstau" only gets 20 hits, so why am I being so picky? ;-P)

Was thinking there must be a set term for this and hoping someone out there in LEOland knows what it is. Otherwise I guess I'll just go with bottleneck.