“Availability replaced from the page”

What Google's message means

Automatic improvements found the page and the feed disagreed on availability and used the page's value. The product kept serving.

Shoppers may have been sent to a product the feed said was in stock but the page said wasn't (or the reverse, losing sales). When Google cannot read the page, the fallback is a disapproval for mismatched availability.

The fix in Shopify

1. Products → the product → each variant → Inventory: quantity matches what you can ship, and ‘Continue selling when out of stock’ is ticked only if you really take orders for it. Save.
2. Keep Automatic improvements → Item updates → Availability on in Merchant Center (Settings → Automatic improvements).

The fix in WooCommerce

1. Products → the product → Product data → Inventory: Stock status (In stock / Out of stock / On backorder) — or Manage stock with the real quantity. Update.
2. Clear the page cache after stock or price changes (WP Rocket, LiteSpeed Cache, W3 Total Cache → Purge all), or Google reads an old copy of the page.
3. Keep Automatic improvements → Item updates → Availability on in Merchant Center (Settings → Automatic improvements).

What it costs while it's down

Nothing is out of Shopping today: the product still serves. If Google can no longer correct it, the listed price of every product flagged this way drops out until it's fixed; a free scan names each one.