Yes, I have the old price set. The product displays a sale ribbon in the upper left hand corner, but does not appear on the On Sale tab.
Thank you for your reply!
In case the Old price is set and the Price is smaller than Old price, the product will appear in the Smart product collections section. However, if you dont have a Price smaller than Old price, but only a tier price, the product wont be considered on sale, thus, wont be displayed.
If you are going to use the tier price functionality instead, I can advise you to not use the On Sale
order method in our Smart Product Collections plugin, but rather a custom list and assign the products which will be considered on sale to it.
Let me know if you need any further advice.