It's possible that this divergence is related to the Holidays registration in VTEX platform. Whenever there's an error associated with the number of days of a holiday, for security reasons, a range is defined by the system that may be affecting the delivery date of your order.
If by registering a holiday, you fill in the Date field correctly, but miss the End Date field, and the holiday ends up being 1 year, 6 months or any undue period, the system understands that there was a registration error and sets a smaller range, defined by it, to release the delivery of that order.
In such case, the order may have the estimated delivery date for the first available business day set by the system.
So if you have issues related to incoherent deadlines or disagreement between the promised date and delivery date, check out the Holidays feature in your store Admin: