There seems to be a problem with the sitemap submission process, going back at least to the beginning of last July. The last note on that thread was posted just a few days ago, saying no change in the commenter's situation. There are several other threads if you poke around, but that seems like the longest-running one and I've seen an employee refer people back to it, so it might be the one to watch if you want to track any developments.
Given that this is still occurring despite being identified as "minor" by JayGon, it looks like it's low priority and you'll just have to wait. Keep in mind, though, that sitemaps are primarily helpful suggestions to the search engines. As long as your pages are reachable via links somehow, they should still be indexed, etc.