I am having this exact same issue on my Series X and was going to post it myself. I’m glad you already have.
It is much easier/comfortable to crouch with the right stick using alternate button mapping by switching B to melee, but when it interferes with ammunition swapping, I have no choice but to switch back to default settings.
I want to play with B as my melee and I hope they see this and can give a quick fix to prevent the knifing action when switching ammunition attachments.
It doesn’t force you to crouch when using the default B= crouch when you switch ammunition so I hope it’s an easy fix.
Same on PS5 - pressing ‘O’ to change ammo type in plus menu causes me to exit plus menu screen and perform a melee action. the ammo type remains unchanged.
