Anyone familiar with the breaking issues from the last version upgrade for plugins? Looking for where to begin bug hunting

One of our community built a very cool plugin which we built our platform around called Docuss. It integrates Discourse into a ReactJS website, unleashing Discourse’s powerful community building and discussion tools onto any existing site by adding a line of code for users to click and enter into a forum thread.

The 2.8 version update broke the plugin and the creator of the plugin isn’t actively coding anymore so others in our community are going to debug and maintain it. Finding a starting point is difficult though and i’d be very appreciative if anyone who is familiar with the latest version update and what breaking issues occurred with other plugins as that will likely be a huge help to begin wrapping our collective heads around what change has broken it and how to update.

Here’s the Docuss plugin
The readme we’ve created for it

Any ideas?