New GitHub repo is not syncing with Jira project

[tim.wheeler]

We have recently created a new Jira project and a related GitHub repo. We have been using both for several weeks, but they do not sync up. We have three other Jira projects and two other repos that are all syncing as expected. 

I have tested that using the new Jira project I can sync commits with another GitHub repo. So the issue lies in the new Repo. Are there any known issues with certain repo definitions not working with Jira?

I didn't create the Repo but it does appear slightly different. It is using a 'MIT license' and has "Restrict editing to users in teams with push access only" selected.

This is Jira Cloud using the GitHub app to sync.

Any help much appreciated.