ERR_CONNECTION_RESET (Impossible to add the product to the cart)

[profacer]

Hello,

I am experiencing a problem when I click the "Add to cart" button.

Prestashop version: 1.6.1.17

The Ajax cart option of the blockcart module is enabled.

Sometimes the "Add to cart" button works fine but sometimes it gives this error:

Impossible to add the product to the cart.
textStatus: 'error'
errorThrown: ''
responseText:

Developer mode is enabled and in the console log the following is displayed:

I will be really thankful if someone can help fixing the problem.

Thank you!

Edited February 15, 2018 by profacer (see edit history)