A 45 day lock will cost the buyer more in fees (points) and or higher rate than a 30 day rate.

If the loan gets locked for 30 days on October 28th and the close of escrow is one month later, that is exactly, oops 31 days, setting up the scenario you describe. Lock expires a day early.

Ah, but you asked for a GOOD reason. Failure by a loan officer to understand how the calendar works is not a GOOD reason.

someone is not paying attention would be my guess, they could have easily extended it. the mortgage officer and teh buyer should have been keeping watch...