AJAX error 200 on almost every Drupal sites

I have no clue on what's going on!
On almost every Drupal site i made, i get this error if i click on any field in Views:
An AJAX HTTP error occurred.
HTTP Result Code: 200
Debugging information follows.
All forum posts about this kind of error dates back to 2011-2014 or says to disable jquery update.
The thing is:
- Some sites don't even use jquery update
- Some are up to date (7.44, Views 3.14
- Tried changing jquery version from 1.7 to 1.10
- Sites are on different hosting providers
This problem dates back to 1 week... 2 weeks maximum.
Made a local copy of one of the sites to disable modules 1 by 1 and guess whar? Views works fine on a local copy.

It seems i'm the only one with this problem
Any clue?