Hello, Jake
Our development team has looked into this. I can confirm that the app continues to work on the instances where it was already installed. We just tested an install into a new instance – it works too.
We did discover that if cookies are disabled for https://time-tracking-confluence.herokuapp.com it will indeed present an empty page. Please allow this site in your browser settings and it should work for you.
I do not believe we have changed anything recently and we do have multiple customers using this app just fine. This app was commercial and paid for a long time too, so no "paywall is coming" as it was already there.
Are you able able to send your findings about "looking at the HTML source, it appears that the coding was intentionally broken" to our 24x7 support via support@techtime.co.nz?