We've just migrated from Magento 220.127.116.11 to Magento 2.2.8. We noticed in the last couple of days some orders are created without billing any tax. When We go check the product We notice the tax class is set to "None" (0 tax) so we change it back to our custom tax ("Taxable Goods") and later We notice new products (sometimes the same) go back to "None".
We were able to check every product with "None" as tax class by running following mysql command:
SELECT * FROM `catalog_product_flat_6` WHERE `tax_class_id` = 0
Even though We've updated them to our tax_class_id We noticed each time We run:
php bin/magento indexer:reindex
4 item's tax class change to "none".
We don't know where to look at this issue. We didn't customize Magento in any form and There are no issues in log files.