[Hueman] Social links not working – what's wrong?

Hello, I’ve got a question concerning the Hueman theme (2.1.7). I want to add my social media channels to the website but apparently the “Add New” button in Social Links section won’t work.

Each time I click it either nothing happens or a new white page is loading – and it keeps on loading but nothing more. I’ve tried to edit it using 3 computers and 3 browsers (Chrome, Mozilla, Explorer), but it is still not working, so I guess it has something to do with my plugins or system or… I don’t know what. I’ve tried on Windows XP, 7 and 8, my Java is up-to-date and enabled.

I have no idea what may cause this, so if you can help me, I’d appreciate it a lot ?? Of course I can list you all the plugins in use or other things as far as my (not expert) knowledge allows me to

my website: https://soszal.net