The Project Support blog today published a post about a pretty nasty bug that has been found in Project Server 2013 and until very recently in Project Online that could cause you to lose resources across schedules. Full details of the bug and the actions you can take to address the issue if you have encountered it can be seen at http://blogs.technet.com/b/projectsupport/archive/2014/02/06/project-server-2013-and-project-online-what-happened-to-my-resources.aspx. If you have encountered any issues with lost resources including resource names turning into numbers, or mysterious material resources appearing, I would highly encourage you to read the above blog.