Laravel 5.4 POST method stop working when cloning site to development server

For the first time since using Laravel I'm facing up a really strange situation:

I've made a website using Laravel 5.4 and everything is working fine with it for a couple of years. Now I need to add some features, and, by the way, make an upgrade to 5.5LTS version. So I've cloned this website to a linode instance that I use as development server, and suddenly no every form that has a POST method stop working. It means login form, contact form, add to cart, order form, etc. Ajax get request are working fine.

Linode is runing PHP 7.2.9 while production server is running PHP 7.0

I had try cloning to a similar configuration than production server using PHP 7.0 and I got just the same fails

Exactly the same is happening on my local machine using valet 2.1.1 with PHP 7.2.6

To check where the problem is, I have added some breakpoints in controllers but none of them are even reached, it seems that when click on submit button the form in question makes a request but immediately resets to empty again. So no POST route is firing its controller method.

Testing server is http://45.33.17.138/sm/public

via Chebli Mohamed