I have this problem and i can't save anything when i'm working in Gantry5
It's a clean installation with Joomla 3.6.5 and Gantry 5.4.1 theme Hydrogen (althought it happens in other themes)
1)When you try to save a default style, this bug happens:
Uncaught SyntaxError: Unexpected token < in JSON at position 93
at parse (<anonymous>)
at new constructor (main.js?5852a6df:10)
at XMLHttpRequest.l.onreadystatechange (main.js?5852a6df:10)
constructor @ main.js?5852a6df:10
l.onreadystatechange @ main.js?5852a6df:10
2) When you save a layout, this bug:
Uncaught SyntaxError: Unexpected token < in JSON at position 37
at parse (<anonymous>)
at new constructor (main.js?5852a6df:10)
at XMLHttpRequest.l.onreadystatechange (main.js?5852a6df:10)
constructor @ main.js?5852a6df:10
l.onreadystatechange @ main.js?5852a6df:10
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