Got any ideas how to resolve this?
Sorry, I have no idea. Also, the link you posted has no mention of any [firstchild_redirect] and it’s also posted on the C# section of stackexchange and not PHP which is what WordPress and WP Themes are made of.
This appears to be a code issue when the theme is used on a Windows Phone.
Does my site (ronangelo.com) display the same issue when viewed on your phone?