App Keep alive always

This version is OK (no errors)
I simply compiled the new .aia and installed the apk, without changing any settings.

Then I made little changes : I added a clock and TinyDB component, so now the app writes the current time on TinyDb every 10 seconds.
I started the service and turned off the screen.
After some minutes I turned on the screen and checked the TinyDB records.
When screen was off, the clock.Timer didn't write any record............

Then I tried enabling notification and disabling battery limitations.
No luck.

Extension Wakelock is not needed ?