App service information is slow to propagate to all of our edge proxies. We’re working on this, but it’s a big hairy architectural problem.
When you’re running an app with a single VM, this can slow requests or 502s during a deploy. The first VM will go away, our edge proxies won’t all know that, and they won’t have seen the new VM yet. If you’re running two VMs, you probably won’t have this issue – but only because it takes longer for both old VMs to go away and gives the edge proxies time to “see” the new ones.