We've seen this more than once. After an online instance has been upgraded, the labels for the Sub Areas on the main menu -- Sales sub, Service sub, Marketing sub -- are missing. What you see instead of, say, "Customers" is "Unknown956"
-- or any 3-digit number.
I had created a 30-day trial site to test the upgrade. I exported the sitemaps from each the Dev and the upgraded Prod. The Dev displays correctly. The xmls are quite different.
Is there a known problem with upgrading the site map when going from 2011 to 2013 online?