You may occasionally see orders that look like they should have split, but didn't.

This can be caused by the following chain of events:

1. Rules only fire when orders and/or order items are created.

2. When the order was created, all of the items were fulfillable.

3. By the time that order was batched, other orders had depleted that stock*.

For Example: You have 100 Orders for Item A, but you've only got 50 in stock. At the moment of creation, each of those 100 orders will see that there's stock, and think they're fulfillable. Stock is allocated during batching. Then, the last 50 orders move into Insufficient Inventory.

It is advisable that you routinely check the results of your auto-split search to ensure that orders newly splittable haven't been passed over.