johnbradford on "Unable to access wp-admin"

Looking at webpage: https:\hbb.org.uk I can see the black "logged into admin" bar but when I click on Dashboard or any other admin link I get:

Waing: Unknown: failed to open stream: No such file or directory in Unknown on line 0
Fatal error: Unknown: Failed opening required '/tmp/pre.php' (include_path='.:/usr/newage/lib/php') in Unknown on line 0

Updated to WP4.5 & experienced major slowdown in performance, in fact I wasn't sure it had upgraded accurately.

Received several

mysqli_query(): MySQL server has gone away

error msg's.

Have tried rebuilding from fresh download (after backing up via Filezilla download of site). Website is still running very slow, but is at least online.

I'm about ready to roll back a couple of days (just to be safe) and just not do anything, but at some point will have to upgrade for security updates.

Any thoughts?