I do not know if it's because of the latest Wordpress update, but the backend is causing problems.
When I try to access a plugin ( Contact form 7 ) this appears:
Fatal error: Uncaught Error: Call to undefined function mysql_real_escape_string() in ...
And here some file paths start. Can anyone give me a clue?
The problem is that this plugin is using mysql_* functions that have been deprecated / disapproved ( in PHP 5.5 ) and completely removed ( as of PHP 7.0 ).
If you updated wordpress or the server, the PHP version has been updated and the support for mysql_* functions has been removed and the plugin has stopped working because of that. One possible solution would be to update to the latest version of the plugin, which is probably already adapted to the new requirements.