A shopper always sees one checkout, decided by your segment rules - so "wrong" rates almost always trace back to which checkout they matched.
What's happening:
They matched a segmented checkout. If a live checkout has a segment the shopper meets (e.g. State is NY, Customer order count is 0), they see that one - and only its methods.
They matched none, so they got the Default. Anyone who doesn't fit a segmented checkout falls through to your one segment-less Default checkout.
Overlap. If two live checkouts could match the same shopper, the result can look inconsistent - which is why PDQ blocks setting a checkout live when its segments overlap exactly with another.
What to check:
Open each live checkout and review its segments - does the shopper unexpectedly match one?
Confirm you have exactly one live Default (segment-less) checkout as the fallback.
Make sure the methods/prices you expected actually live in the checkout that shopper matched.
💡 A quick way to test: recreate the shopper's scenario (order count, destination) and see which checkout its rules point to.