For me, it happened following a re-import of many addresses (deleting old addresses and adding new ones). Orders have duplicated in two others orders( first order with an address deleted and the second order with an address activated).
I managed to reproduce the problem by logging into a customer's account. The customer already had items in their cart when I logged in and I added another item after my logged in.
When I validated the order, this one is duplicated in two order:
- First order: with a deleted address and the items that were already in the customer's cart when I logged in
- Second order: with a valid address and the item I added after my logged in
I think that prestashop has associated in the cache the articles already in the basket with the old address. Then the client disconnected. I delete the old address and create a new. When i logged in i add a new item, prestashop associated in cache this item with the new address. And after validation, order was split because old items is associated with old address and new item was associated whil new address.
I deleted my site's cache and will see if it reproduces in the days to come. If this is resolved I will come back to post on this topic.