After updating from version 6.5.8.12 to the latest version (v6.6.4.1), I encountered an error message on the frontend. The error message displayed on the shop pages is:
SQLSTATE[42S22]: Column not found: 1054 Unknown column 'cart.payload' in 'field list'
We just ran into the same issue. The problem is caused by a wrongly implemented database migration (\Shopware\Core\Migration\V6_4\Migration1648709176CartCompression). I expect you didn’t run bin/console system:update:prepare and bin/console system:update:finish on your shop and just execute the database migrations via bin/console database:migrate --all. The missing payload column will be created in an updateDestructive method which will not be executed when you only run bin/console database:migrate --all. Like the documentation says only destructive database operations should be executed in the updateDestructive method, but shopware also creates the new column there and not in the update method.
In the update() method you implement non-destructive changes which should always be reversible. The updateDestructive() method is the follow up step, that is run after update() and used for destructive none reversible changes, like dropping columns or tables. Destructive migrations are only executed explicitly. Database Migrations | Shopware Documentation