Sort order on the search results page seems to be working for me in Firefox and Edge on a desktop PC.
Try another browser to see if that feature loads correctly.
If it does, go back to your original browser and try clearing your cache and eBay cookies. In some cases an overly aggressive ad blocking rule can affect certain page features -- try temporarily disabling to see if that makes a difference.
If you run into that problem and are unable to change the sort order on the search results page, use the link to the advanced search page -- you should be able to make changes there and apply those changes directly to your search results that way.
