I believe that Bitwarden issues a virtual mouseclick into the checkbox field after the auto-fill action has been completed, and that this is the source of the problem. The event listeners on the Amazon login page apparently toggle the state of the checkbox when it is clicked. Fortunately, this allows for your problem to be solved:
Create a custom field of the Boolean type, named rememberMe. Set the state of the boolean to false, by leaving the checkbox cleared. This works, because Bitwarden will now auto-fill the checkbox as false, but the virtual mouseclick will cause the state of the checkbox to toggle to true.
Let us know if this worked for you (it worked in my testing, on a Chrome browser).