Thanks @kurt
I wasn’t aware of that condition of shared CPU VMs being booted. Is that documented? I don’t see that on the pricing page. I get that you are paying for a slice of a CPU, but figured that slice would be all the time. Not a slice of a CPU only if one is available.
Thinking about it, that would also impact auto-scaling since there would be no capacity to auto-scale into. So even if more instances were needed, they wouldn’t be created. And requests would fail. Hmm.
It’s good they are going to be kept longer but it’s a concern if you have to hope another client gives in first and deletes/moving their app in order to free up capacity (as it sounds like happened here by a customer migrating away). Whether it will happen for a third time … I guess that is the question. It’s a nice problem for you to have. You must be growing faster than you can buy more servers 
Regarding backup regions … I was going to remove that cdg as per your recommendation App starting in backup region - #2 by kurt but forgot and left it. Though it appears not to have helped in this case (which seems the perfect case for a backup region) would your advice now be to have backup regions … or not?
Thanks.