In case you've enabled the 'Sold out products last' feature, but there is no change in products' order, you might start with checking the following:
Check the Jobs queue
If you have recently enabled the app for the first time, or recently made some changes to the settings, then your job may be queued or still running. You can check on the queue by clicking on 'Jobs' in the app sidebar:
The time it takes to complete a job will depend on the number of products in your store, and the features you have enabled. Shopify applies a rate limit to external apps, so our app processes around 2 items per second.
Check the collections sort order
The 'Sold out products last' feature works for collections set to Manual, Random, and Trending sort orders only.
Please note that the Trending Sort option is just a manually sorted collection also, just that we update it with our app.
The reason that only manually sorted collections can use this feature is that you cannot change the order of any of the items when they use one of the built-in sort orders (A-Z, Price, Best Sellers, etc). Shopify does not allow us or anyone to do this.
One thing to keep in mind when using the 'Sold out products last' feature, is that any sold out items will be moved outside the top 1000 products, or last if there are less than 1000 products. This is a limitation of the Shopify platform, our app can only modify the sort order for the first 1000 items in a collection.
If you have any further questions, please reach out to us in the live chat or at firstname.lastname@example.org, we'll be happy to help!