I don't work at Github but I'd read here recently that they've been undergoing a herculean migration from whichever cloud provider they were on to Azure since their Microsoft acquisition, and that it coincides with an increase in outages. I'm guessing that the solution here was probably just to not do that and it's too late.
Yes I would image the issues are due to doing a migration period. Not the fact that it's moving to Azure in and of itself.
They weren't on any cloud provider previously. They famously had their own "metal cloud" of managed servers with everything being containerized and managed by Kubernetes. It seemed like it's worked pretty well, especially for their complex git operation tasks which had specific hardware requirements, but the official word is that apparently they're running into scaling limits with finding new datacenter capacity.