Found it! Somehow you managed to record an element name that has a special symbol in it - see attached screen shot. When we go to generate the pages.g.cs file we strip the special symbol (it's not legal in code) which results in a name conflict with the other already existing "TableCell" element.
Fortunately the fix is easy. Just change the name
of one element or the other so that it doesn't result in a name conflict.
I'm also filing a problem report using your project as an example so that our development team can prevent this conflict from happening in the future.
P.S. you can cut the size of your project folder in half by deleting the Backup folder. It looks like an old backup copy that is no longer needed.