PHP error message in nav_menu.php

[ Moderator note: moved to Fixing WordPress. ]

Hi,

and HELP, I’m desperate: I can’t access the Customizer or the Design/Menus of my WordPress website https://www.steamrebels.de anymore. This website is about our newly opened vaper shop, and it is really important for us to gain new customers. I’m crestfallen…

The Customizer only shows a blank white screen. If I try to access the main navigation menu via Design/Menus, I get this error message:
Parse error: syntax error, unexpected end of file, expecting ‘,’ or ‘)’ in /homepages/18/d428354023/htdocs/steamrebels/wp-admin/includes/nav-menu.php on line 579″

Any idea what’s amiss here?

It seems to me the error is ocurring since the recent WordPress update to version 4.7.5, but I’m not sure.

And here is some additional information: I’m using using a Twenty Sixteen Child Theme, but the error remains if I change back to the original Twenty Sixteen theme. My server PHP version is 7.0. My plugins are all up to date. I have disabled all of them for a test already, but the error remains. Right now, only the WP Statistics plugin is active. Yoast SEO is disabled, all other plugins I have deleted alltogether.

I’m really looking forward to your advice. Thank you so much for your support!

Regards

Astrid