I upgraded my site at
https://www.starch-smart.com to Joomla 3.6.4 and had my home page disappear with a JSON error.
By trial and error I discovered that the problem appears to be caused by a module of type EasySocial Users that is in the grid1 position on the home page.
I have disabled that module for you to take a look.
The name of the module is "Recent Member Visits".