The updates nobody reads, and why
Long updates get skimmed, and skimmed updates get misunderstood. If your weekly note runs past a screen, it is functioning as a record for you rather than information for them.
Two other failure modes are worth naming. Updates full of activity rather than progress — a list of things you did that does not add up to a statement about where the project stands — leave the reader unable to answer the only question they had. And updates that never contain bad news stop being believed, because no real project runs clean for two months. A note that occasionally says something slipped and here is the new date is more credible than an unbroken run of green, and it makes the eventual genuine problem far easier to raise.