Draft Order Checkout Incorrectly Saying Product Is Sold Out

[LucidCandle]

When I send a customer an invoice to pay from a draft order, they are getting an error message saying that the items are "sold out" and that there are "inventory issues" but this is incorrect. Not only do I have lots of inventory of the products, they are also set to "continue selling when out of stock". This has never happened before and is preventing me from operating my business. 

[LucidCandle]

It appears that this happening only to products that I currently don't have included in any sales channels. There are products that I reserve only for special customers that I don't want listed on my general website. To prevent them from appearing I don't include them in any sales channels but can include them on draft orders. This has worked well for over a year and now all of a sudden the checkout isn't working because of "inventory issues". Is this a Shopify bug or did they change their system in some way?