First of all I couldn't give you debug info because I have no idea where the hell did you put the Debug info button with the current menu. You could really add some clarity to that.
I made a custom Error 404 layout, but instead of that, I get this message when I navigate to a non-existing page:
Not Found
The requested URL /srg was not found on this server.
Apache/2.4.7 (Ubuntu) Server at medellic.com Port 80
Medellic.com is my website, of course. Is this some server-side setting that prevents the custom page from showing up, or am I missing some settings somewhere? The layout is added to the Others / Error 404 page to be used there.
I don't know what you mean by "setting up correct layout".
It doesn't work with the twentysixteen theme either (after integration, of course).
I didn't try this particular Error page with another installation, but I have another website with Toolset and the custom Error 404 page works there. The two sites run on the same server, so apparently that's not the issue either.
2)
*** Please make a FULL BACKUP of your database and website.***
I would also eventually need to request temporary access (WP-Admin and FTP) to your site. Preferably to a test site where the problem has been replicated if possible in order to be of better help and check if some configurations might need to be changed.
I would additionally need your permission to de- and re-activate Plugins and the Theme, and to change configurations on the site. This is also a reason the backup is really important. If you agree to this, please use the form fields I have enabled below to provide temporary access details (wp-admin and FTP).
I have set the next reply to private which means only you and I have access to it.
I don't know what happened but today I see the actual Layout-based Error 404 page. It's strange because I didn't change anything in the settings/updates since yesterday... Anyhow, we won't be able to see what caused the problem earlier, so I mark this thread as resolved.
Thanks for your support.
This ticket is now closed. If you're a WPML client and need related help, please open a new support ticket.