The person waiting on you deserves a useful update, even when progress is disappointing.

Silence during a delay is nearly always read as bad news getting worse. The person waiting cannot tell the difference between a problem and abandonment, so they fill the gap themselves, usually with the least generous explanation available. An update that admits slow progress still lets them plan, and it costs you a sentence.

If someone is waiting on you now, send the honest state of it today: where it stands, what is blocking it, when you will next report. Do not wait until you have good news. The update is the courtesy, not the outcome.