PrestaShop
When trying to log into my PrestaShop backoffice, the page was reloading / refreshing without any errors!
After much investigations (3hours non stop!) I found out this solution:
In the file “login.php” under your backoffice’s folder,
on line 55, you have:

 $cookie = new Cookie('psAdmin', substr($_SERVER['PHP_SELF'], strlen(__PS_BASE_URI__), -10));

where the “-10” value corresponds to the number of letters of “prestashop”, set it to the number of letters of your store’s subdirectory name and your will be back to the business again.
For exemple:
if your store is located at:
https://www.yourdomain.com/store/
the word “store” contains 5 letters, so the line 55 in login.php should become:

$cookie = new Cookie('psAdmin', substr($_SERVER['PHP_SELF'], strlen(__PS_BASE_URI__), -5));

What I found out again, is that Prestashop is a very bad done software and not ready for business. I will switch to a better e-commerce solution!