Amazon showing the wrong expected delivery date for FBM orders

Hello all and thank you in advance,
we are offering UPS ground service for our FBM orders,
we have set up our shipping templet so Amazon calculate the expected delivery date using UPS ground

Amazon is showing the promised delivery date based on the calculation if we use UPS Ground.
but when its time to ship the item we do not get UPS ground as an option when we try to purchase the shipping label directly from Amazon, the reason for that is that the item would not make it on time if we ship with UPS ground, instead, it gives us the option to use UPS 3 day service, even if we ship on the expected ship date.
this happens also for some of the orders that need to be shipped with USPS first class

why amazon is showing the wrong delivery date? basically, you open the order detail, and it will show the buyer choose UPS Ground as the shipping service, and it’s asking us to ship on April 15 for example, but if we try to purchase the label on April 15 it will not show UPS ground, because it will not make it on time if we use that. A
I am not sure if we are allowed to post screenshots of an example.

this is causing us so many issues with the customers, at least 50% of our orders have this problem
contacted support a few different times with no real help, and the last time they told us “You can use UPS ground anyway and it will not affect your delivery date rating ” so they are aware of the issue I guess, the only problem is that customers are getting the order one or 2 days late and they are giving us hard time with feedbacks and returns
anyone notices this issue on their account? we would love to hear your work around it if you have any
thank you!