Unfortunately you will have to contact your hosting support as the problem is with the server, not with Images. Data from login form don't reach php.
I suspect this might be related to incorrect settings of mod_security installed on your server. I have tried to disable mod_security using .htaccess from our troubleshooting page:
https://www.photo.gallery/documentation/trou ... g/#suhosin but this produces error 500.
I have prepared a test link you can send to your provider.
Normally when you fill the form up you will see some data on top, in your case it just comes out empty after pressing login button. No data appear in php. $_POST global variable stays empty.
Please contact your hosting support.