Is it possible that background and foreground are in collision?

on sim it's difficult to simulate it due to fast computer but on device?

or course I have a strange error (as usually recently on epix/f7) that suggesting collision

Nobody knows? :-)

I don't know, but I would be very surprised if this would be possible. IMHO every app runs on 1 thread.

And it can be problem. 2 threads and one storage file.

It's enough background keeps storage in write state.

Not sure what you mean with the foreground calling "onTemporalEvent".  Do you mean you registerForTemporalEvent()?

What are you seeing that makes you think there is an issue?

If you call Background.exit(null), onBackgroundData won't get called until you exit with non-null data

00:00:00 the last onTemporalEvent

00:01:00 foreground  calls registerForTemporalEvent

2 cases

1. 00.05:00 foreground saves data and background reads data in onTemporalEvent

2. 00:05:00 background reads data in onTemporalEvent and forgets to close file at 00.05:01 foreground try to save data

A background services runs for no more than 30 seconds at a time.

What are you seeing when the foreground tries to save?

Are you using setValue()/getValue() or setProperty()/getProperty()?

of course Storage.setValue()