I have exactly same problem.
Click on button just shows same page (URL argument scan_files=1 passed).
Here are some server info:
OS: Linux 4.15.0-45-generic #48-Ubuntu SMP Tue Jan 29 16:28:13 UTC 2019 x86_64
Shell: /bin/bash
PHP binary: /usr/bin/php7.2
PHP version: 7.2.15-0ubuntu0.18.04.2
php.ini used: /etc/php/7.2/cli/php.ini
Also, with debug mode ON I have nothing.
No errors in console, no nothing.
Just page redirect, and instant opening.
Cheers!