This message and the status of Lost/2020 (althought that's a little odd as you likely had to change that manually) typically comes after an Inventory has been performed. Items that were not inventoried will be changed to have a status of Lost/xxxx where the xxxx is the year of the inventory. Now you know why it's a little odd as it should read 2019 at the most. This will be normal if the books are returned to the library it will tell you and then it will circulate the book IN once you acknowledge the message.
If this is an incorrect status, to resolve the issue you need to use your Library File and change search by option to "Status" and look for Lost/2020 or whatever status it is telling you about. Then you can use the Global option to update the status to IN. This will remove any of these notifications in Circulation but it does make your inventory process null and void since you are basically saying ignore these non-inventoried items.