We've reached the stage where architectural decisions are being questioned. Nobody should need to ask me "well why are we using github?" but here we are.
They needed to fix this two weeks ago. The next time I'm in charge of stack decisions I will be evaluating competitors. This is exactly how Slack beat Hipchat.
Don't let weekends dilute your view of the situation. There's only 23 weekdays in March and Github has not been reliable for 5 of them.