When pages are created/moved, the site map cache is cleared by touching a dependency file under /Data/sites/[SiteID]/systemfiles, if for some reason it can't modify those files this could happen. I would make sure the /Data folder is writable by the web process and maybe try deleting all files from /Data/sites/[SiteID]/systemfiles, they should be re-created as needed. Possibly if they were copied from your dev machine they have funky permissions.
Hope it helps,
Joe