WP 4.4 – Custom plugin interfering with front-page.php display

I’ve just moved my own custom wordpress theme (based on _s) and a custom plugin from one WP site to another on a different server. The original WP version was 4.3.2 and the new version is 4.4.

Now with 4.4 all my pages are missing the footer and my custom plugin seems to be interfering with the output of front-page.php: When activated most of the content does not appear:

http://venturecentre.org.uk/venturecentre-wp/

FYI – I’ve used the custom plugin to include all the extra custom post types, functions and widgets that I’ve added on top of the original _s theme, as advised in this useful article – http://www.wpbeginner.com/beginners-guide/what-why-and-how-tos-of-creating-a-site-specific-wordpress-plugin/

Not quite sure where to go from here, any advice?

John