If you're using the Product Upload section, Product Builder collects available inventory for all products in all bundles if inventory management is set to "Shopify".
It then sets the number of available Custom products according to the number the of products available (so the Custom Product can't be purchased if there is not enough products in stock).
The moment a customer purchases your Custom product, inventory of all products (where inventory management is set to Shopify) is decreased. The app need's to prevent other customers from purchasing the same product at that point and changes are reflected in the inventory.
Inventory is decreased when a customer confirm's the order, rather than before. If two customers were trying to buy the same product (as part of a Custom product), this mechanism will prevent both customers from buying and only allow one customer to purchase the configured Product. When an order is cancelled, inventory will be increased back to their previous levels.
If you are experiencing specific issues with your inventory, send an email to Support@Agile.haus, with the following information:
Custom Product URL
Any relevant backend variant links from the problem bundle
Screenshots if needed