Hi Dirk,
Thanks for posting the question on the community.
Just to give you a high level overview of how Mobile SDK works, here are few things.
1. Mobile SDK is utilizing Keychain Services for iOS, and Keystore and Account Manager for Android to persist, and manage all credentials which are provided by Apple, and Google for the most secure storage solution in Mobile Operation Systems.
2. For upgrading scenario, if the application was not uninstalled, and re-installed, the SDK will persist the credentials upon upgrading the application by design. When it was removed from the device, and reinstalled, the credentials may get wiped out.
3. If you are using iOS SDK version below 1.6.00, then was upgraded to the version above 1.6, you may experience re-login enforcement from Mobile SDK due to the change that we have made in 1.6 to improve device registration process.
So, from my understanding, the only situation where you will experience re-login upon reinstallation is when you were using the SDK version below 1.6, then upgraded to above 1.6.
Just for us to help you better, if you could please provide us information about your environment, such as SDK version, MAG/OTK version, that would help us to investigate and identify the root cause of the problem.
Thanks,