The delay needs a question before it needs an accusation.

An accusation ends the flow of information. The moment someone has to defend themselves, you stop learning why the thing did not happen, and whatever explanation follows is shaped by self protection rather than by what actually occurred. A question keeps that channel open and costs you nothing you cannot spend later.

Open with what you genuinely want to know: where it stands, what is blocking it, when it can be finished. Say your own position plainly if the delay is hurting you. Keep the harder conversation in reserve, since it may turn out not to be needed.