I've only just re installed it today so won't be able to check for a few days whether a re login is required.
As I said earlier a login would last several days but would then cease and ask for a re login.
That's also consistent with an ipad device I have so it's nothing to do with the device.
The software developer will have the definitive answer as to what triggers the requirement to login again, I am just astonished no one knows what it is.
Whatever the answer I can't see why the app can't be logged in indefinitely or like most ios apps it can be linked to the device password so that it can be accessed with fingerprint or facial recognition.