Yesterday everything is ok, then I do nothing but now:

Whoops\Exception\ErrorException thrown with message “Call to a member function filter() on null”

#0 Whoops\Exception\ErrorException in /home/wwwroot/user/plugins/admin/classes/admin.php:471

and there is the error: “Cannot connect to the GPM"

Can you check these common causes of GPM problems?

But the thing is - everything is ok before, and I have NOT do anything to my site files.

Something must of changed, perhaps a file got deleted? Perhaps something changed on the sever? PHP version, modules, etc?