Inventory in MBC Bundles is tracked per component, not as a single "bundle" stock figure. Selling a bundle deducts from each component individually, and the bundle is out of stock as soon as any one component has no stock in a variant that belongs to the bundle.
The bundle list flags this with a Bundle out of stock warning, alongside warnings on the specific components. Start there — it tells you which item is actually empty, which is usually the whole answer.
How the stock figure is arrived at
Stock is summed across all of your locations, and deduction starts at the first location and continues into the next as stock runs out. So a component isn't out of stock until every location is empty.
If a component looks stocked in Shopify but the bundle still reads out of stock, check the Locations setting — it restricts which of your locations bundles are allowed to draw from.
What the out-of-stock display modes do, and don't
Three modes control whether the widget is shown: Show the widget only on product pages of in-stock products, Always show the widget even if some bundle products are out of stock, and Hide the widget if any bundle product is out of stock.
They control visibility only. None of them changes what the Add to cart button says, and none of them makes an empty component purchasable — switching to "Always show" gets the widget back on the page, with the bundle still unbuyable. "Bundles with out-of-stock products" covers the three modes in full.
"Out of stock" and "Pre order" are two different captions
The button reads "Out of stock." The bundle as configured has no purchasable combination. Restock the component, or change the out-of-stock display rule if what you wanted was for the widget to stop appearing.
The button reads "Pre order." Shopify reports the selected item as out of stock but still purchasable — which is how an item with inventory tracking turned off is reported. Either turn inventory tracking on for that product in Shopify, with stock on hand, or rename the caption in Widget customization → Text settings → Products, for each language your shop has added.
One detail there we haven't independently verified: whether Shopify's Storefront API specifically returns "currently not in stock" for variants that simply have inventory tracking disabled. That is Shopify's own behaviour rather than something the app controls; everything else in this explanation is confirmed in the app's code.
Does re-saving the bundle help?
Sometimes, and only on one bundle type.
Physical bundle. Saving it again rebuilds its generated Shopify product from current component data, so it's the right move when the bundle's own product page disagrees with what Shopify shows for the components. A Physical bundle is only rebuilt on its own when a component's variant list changes length — a variant added, removed or renamed — so it can sit on stale data indefinitely otherwise.
Shopify bundle. No need. A component product change triggers a rebuild automatically on this type.
Widget-only bundle. Re-saving changes nothing — there is no generated product to rebuild, and the widget already reads live data.
In every case, re-saving doesn't create stock. If the component genuinely has none, the bundle stays out of stock until you restock it.
If several Physical bundles on your shop are showing stale data at once, contact support and ask for a shop-wide resync of your Physical bundles, rather than opening and saving each one individually — there's no button in the app for that.
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