RM Click&Drop fulfilling entire orders from one location where stock is not available

We have 3 locations.
Occasionally orders are partially fulfilled from one location, and the remainder is fulfilled from another location. Up until this week, we were able to do this with no issues, and the Royal Mail Click&Drop would know that just the items being fulfilled from your current location would be included in the delivery.

This week, Click&Drop has all items on the order included - which is then fulfilling the entire order from 1 location (warehouse) on Shopify, even when the stock is not available.

Image attached is what it should look like, but when I printed the Click&Drop label for this order, it fulfilled all 9 items from BLT Berkhamsted, rather than just the 8 that it should from this location. This then returns the stock to the inventory of TTC Pulloxhill and marks stock at BLT Berkhamsted as -1.