App not showing system that's already set up
I am having the same problem--also on iOS 15.2.1. The problem has nothing to do with trying to login to two accounts at once. I can login to a second account from the app and can see the basic account information. However, the app does not see the installed SimpliSafe system. It opens to this screen:
Welcome to SimpliSafe
Let's set up your security system now.
<Set up System Button>
If you press the button it asks you to enter the site name and continue with the initial setup.
The system itself is still working fine. I confirmed that test signals are being received and the history and configuration all look fine if I login to the account from a desktop browser. However, the app on the phone doesn't think there is a system installed on this account.