Problem is when the released product is configured to direct delivery. It ignores the stock in the sourcing company to calculate ATP dates. It seems the problem is the sourcing site in the sales line.
The ATP delivery date calculation when the sales line is created does not work OK, if the released product is configured for automatic direct delivery.

Repro steps:
Contoso, company USRT, Item A001
1. Configure the item so every time a sales order is created, it will create a direct delivery from USMF:
Go to released product A001, edit, tab Deliver, and set Direct Delivery = Yes, Direct Delivery warehouse = MIAMI.
Default supplier 9001 (intercompany, company USMF)
2. Create a new sales order:
Company USRT, Customer 004005, Delivery date control: ATP
Item A001, quantity 100
3. Check ATP
Go to the sales line, tab Sourcing. Delivery type changed to Direct delivery, that's OK. But the field Sourcing site is EAST. That's wrong, EAST is the site in company USRT, and it should be a site in USMF. Sourcing warehouse is empty. that's wrong as well.
And if you check the delivery date, it ignored the stock available in USMF.
If you clicked on the delivery alternatives button, you will see the right delivery date. Delivery alternatives button works fine, however the ATP delivery date calculation when the sales line is created does not work OK, if the released product is configured for automatic direct delivery.