Sorry for the delay. WooCommerce was the only active plugin besides my shipping rate supplier (Shippo). It’s clear Shippo is providing rates. The problem is when any change is made during the checkout phase that requires a refresh, so any address change or selecting a different shipping method, all shipping methods are lost.
I also tried disabling the local pickup option within WooCommerce settings to see if that was interfering, but there was no performance change.