All Ajax calls suddenly stopped working with parseerror

[rook]

Hello,

I need some urgent help. I would appreciate if I could get some guidance.

Up until yesterday, our prestashop 1.6.1.11 was working well but suddenly the Ajax calls stopped working.

 

Now we have an issue where search is not auto-suggesting (because it is ajax based), ajax cart throws error, login throws error (in one page checkout), we cannot add/remove products from backend order screen, etc

 

So in short all the ajax calls have issue

 

We run the prestashop on google cloud platform. We get following errors:

Ajax cart error: 

Impossible to add the product to the cart. blockcart.
textStatus: 'parsererror'
errorThrown: 'SyntaxError: Unexpected token < in JSON at position 0'
responseText:

 

Login error:

TECHNICAL ERROR: unable to send login informations Details: Error thrown: [object Object] Text status: parsererror

 

Appreciate the guidance