It's a fundamental problem of open source projects hosting on GitHub. I don't think the the Fossil colocation model is necessarily right, but some open protocol is needed so that issues can be easily migrated between these services.
As others have pointed out, this is Gitlab. When it comes to github, they previously helped me transitioning a bugzilla into github issues, but it doesn't look like they do this anymore.
Back then, I managed to get approval from all our contributors/issue authors so that their individual bugs and comments would show up as their individual bugs and comments, as well as retaining issue numbers.
That's the one Github staff helped me use (though there were no public endpoints at the time). I recognize some of this. I don't think it's supported anymore.
