We have a weird issue right now - we are using the ShipperHQ extension and MSI within Magento. Stock is handled correctly by Magento, but when we go to checkout, no rates are returned because the ShipperHQ extension is seeing a "false" value returned when it checks for the stock status of the products.
The MSI setup has a FBA location and a store warehouse location, both of which have appropriate stock levels.
Magento itself, when doing the stock checks, works fine. The last hiccup is with ShipperHQ.
We don't use the default source because we want to offer in-store pickup, so we had to create the appropriate MSI setup.