Earlier today Shopify tested a new feature for their queue that tells you some important information that’s going on behind the scenes. This includes if your size is in stock and how long you are expected to wait in queue. This level of transparency is super helpful.
The team will work on documentation on how to handle this (ie. what do I do if my size is sold out?) and compile that once we know this feature is live everywhere. As of right now it was a single test but look for this to go live over the coming weeks!