Hi @moondory77 ,
Yes, you observed correctly.
During the data migration portion of the deployment (which occurs after the system has done a bunch of validation and consistency checks), the system temporarily disables your app to do the actual data migration.
This is to protect the data integrity of your app - as your app's metadata, reference data and cloud code scripts are all changing underneath it. So we disable the app, make the changes, and re-enable the app.
All of this normally takes just a few seconds - though it does depend upon the number of changes being made.
I hope that helps to clarify things!
Paul.