Hi. I don't know it is a B4A behaviour.
How to reproduce:
Install attached app
When finished, click 'open' button (see photo)
Press 'Click' and go to second activity
Press Home Button
Reopen app again from launcher/applications list
App restarts and goes to first Activity, in log appears: Killing previous instance (main)
Press 'Back button', Activity 2 now appears
If when app installs I click 'Done' it works well
How to reproduce:
Install attached app
When finished, click 'open' button (see photo)

Press 'Click' and go to second activity
Press Home Button
Reopen app again from launcher/applications list
App restarts and goes to first Activity, in log appears: Killing previous instance (main)
Press 'Back button', Activity 2 now appears
If when app installs I click 'Done' it works well