Interesting development on on 1.5.8a site. PHP 8.0 OPC bootstrap
Guests and new users can check out fine.
Existing Customers are getting
[##############################] Either the available shipping options or your chosen shipping method's price has changed. Please re-select/review your desired shipping method.[/COLOR]
I note that there estimated cost for USPS Ground Advantage is $5.40 for the item while guests and new signups show $5.70.
The only debug file concerns WebPay and it is turned off.
Investigating
Any more info you might need to know?