This is a common issue in Odoo eCommerce when taxes suddenly stop computing. The fact that it started after you changed inventory tracking settings is a clue — those changes may have triggered a product template cache refresh issue. Here's how to troubleshoot:

Step 1: Check the "Prices" setting on eCommerce

Go to Website → Configuration → Settings → Pricing and verify:

• Tax Display is set to your preference (Tax Included or Tax Excluded)
• The Fiscal Position is not overriding or zeroing out your tax

Step 2: Check product pricelist

Go to Website → Configuration → Pricelists and open the active pricelist. Check if it has tax settings that might override the product tax.

Step 3: Verify the tax is still on the product

Open the affected product in backend (Sales → Products or Website → Products), go to the Sales tab, and confirm the Customer Taxes field still has your 12% tax selected.

Step 4: Check Fiscal Position mapping

If a Fiscal Position is automatically applied (based on country/IP), it may be mapping your 12% tax to a 0% tax. Go to Accounting → Configuration → Fiscal Positions and check if any automatic position is removing the tax.

Step 5: Clear website cache

In developer mode, do a server restart or clear the pricelist cache from Settings.

Most likely cause: A Fiscal Position is being automatically applied and is overriding the tax to 0 for website visitors. Check that first.