Just to add to @rossko57’s excellent explanation, in this case you really were not renaming the Items even with the old way. When OH unloaded that .items file it destroyed all the Items that were defined in that file. When it loads a .items file it creates all those Items anew. It appears at first look that you’ve renamed the Item but in fact you deleted the old and created new ones.
There is a hackish trick you can use if you have more than one or two of these Items. See OH 3 Tips and Tricks, in particular the “Editing JSONDB , a last resort”.