Seems to be a lot of undefined Indexes going on and they point to a whole lot of different files. Please let me know what the fix is, once you find it, in case it happens again. The only thing I remember doing is CSS fixes in the Customizer, but I can't imagine that would do anything like this. I am thinking it might have something to do with them changing the Advanced Custom Field stuff since they have access to it, so we might have to do a backup restore, but check with Ryan Ross about that before doing it.