I installed Drupal 8.5.6, in French. It seemed to work well, apart from no CSS working, but I corrected by unchecking CSS aggregation in the performance settings.
I decided to install some modules, one by one. Every time I install a module, after I click on the Install button, I get this.
After waiting more than 2 minutes (which is abnormal to me), I click on the Extend link to see if the module I am trying to install has been installed. The module seems to be installed, since it is checked, but it is not working.
So I uninstall that module, and try installing another module, but I get the same result.
I have also noticed that using Drupal 8.2.5 everything is fine.
Is there any version problem, or am I doing something wrong?
I changed the PHP version using on the host to PHP 7.1.