I don’t work with sitemaps, so can’t really offer any advice there, but this sounds more like a firefox problem. Are you using firefox as your browser?
There are man places in the MainUI especially with newly created items, where firefox caches the old version of the item list and doesn’t refresh it with new items until you do a hard (cache clearing) refresh of the page. These issues do not appear if you use a chromium based browser such as chrome or edge.