Diagnose why a WooCommerce order's stock isn't decrementing

A WooCommerce store noticed a product's stock quantity isn't decreasing after orders
come in. Details:

PRODUCT: [Aria Ceramic Planter, Medium], stock shown as [42] but at least [11] sold
this week per the order list
SETUP NOTE: [product is also included in a "Planter + Plant Starter Bundle" sold via a
bundle/composite products plugin]
ORDER STATUS OBSERVED: [most affected orders are still sitting in Processing, not
Completed]

Walk through the diagnosis in this order:

1. Confirm "Manage stock?" is actually enabled on this specific product, not just at the
   store level, since a product can have store-wide stock management on while its own
   product edit screen has it toggled off, which silently stops it from tracking
   quantity at all.
2. Check WooCommerce Settings > Products > Inventory for the "reduce stock" trigger, since
   by default stock reduces when an order moves to Processing or Completed, not the
   moment a payment is authorized. If orders are stuck in Pending or On-hold (common
   with manual payment methods or a delayed payment gateway callback), stock never
   reduces even though the sale is real, which matches the "orders are stuck in
   Processing" detail above and is the first thing to rule out.
3. Check whether the bundle/composite plugin decrements the component product's stock
   independently, or only decrements the bundle's own stock entry. Several bundle
   plugins by default only reduce stock on the parent bundle SKU and never touch the
   individual component's stock unless a specific setting is enabled, which would
   explain missing decrements specifically on a product that's sold both standalone and
   inside a bundle.
4. Check for a second plugin (multi-channel sync, POS, or a stock-sync integration) that
   might be overwriting the stock number on a schedule, effectively resetting it after
   WooCommerce correctly decremented it.
5. As an edge case, consider whether two orders for the last unit or two of a low-stock
   item were placed within seconds of each other: WooCommerce's stock reduction isn't
   always perfectly atomic under high concurrency, and a flash-sale or a low-stock
   "almost sold out" item is the most likely place to see a real oversell from a race
   condition rather than a settings misconfiguration.

Replace the bracketed product, quantities, and plugin with your own store's setup.