BuyBox appears and disappears

i have a new FBM listing in Grocery & Gourmet Food. i’m the only seller, brand is the manufacturer, product is not sold anywhere else.

the issue: Buy Box shows up fine when browsing logged in, but in incognito it appears for some zip codes and disappears for others (I tested so many zip codes). sometimes the same zip code will show the Buy Box on one refresh and not the next, within the same 3-minute window.

i’ve tried:

– New UPCs and recreating the listings

– Different category nodes

– Bumping stock from 200 to 2000

– Enabling SSA in the shipping template

nothing helped so far. my best guess is something’s off with how Amazon calculates delivery estimates for certain regions, but we can’t confirm that.

has anyone dealt with this before?