Custom built plugin with google fusiontables map broken after upgrade

Hi all,

I have this custom built plugin I use to display an interactive map with a dropdown. It pulls data from an SQL database and shows it in boxes when you click on a country.
Since the WP 5 upgrade, the coloured overlay (made with geojson) on the countries isn’t appearing and unfortunately the dev is not around to give me a hand.

I can’t find any errors in the console and although I have downgraded WP to 4.9.9 it still doesn’t work.

While I’m familiar with aspects of the plugin’s code, I don’t know how to update it to be compatible with the new wordpress. Any ideas?

The page I need help with: [log in to see the link]