Since iOS 15 the App occasionally forgets that it's locked in

[MMilesMM]

Describe the bug
Since iOS 15 the App occasionally forgets that you are logged in. A force quit of the App and relaunching it solves it for the time.

To Reproduce
Launch the app
Use it briefly
Force quit the app
Lock the device and leave it for ~30 minutes
Unlock the device
Launch the app again

Expected behavior
The App opens and remains logged in

Screenshots
Not applicable

Smartphone :

• Device: iPhone 13 Pro Max, iPad Pro 13" 2019
• OS: iOS 15

Additional context
Another iOS Developer has already found the issue: Link to the article

The Short form:
(citing from the before mentioned article): "Starting with iOS 15, the system might decide to “pre-warm” your app before the user actually tries to open it and this can increase the chances of protected data not being available when you think it should be.
Protect yourself from this by waiting for the application(_:didFinishLaunchingWithOptions:) delegate callback, and if possible, keep an eye on UIApplication.isProtectedDataAvailable (or the delegate callbacks/notifications) and handle the situation accordingly."

Another helpful link: Bug report