Main function not called by android service

Hi,
We encounter the following problem:
when trying to use a background android service as in the kdab example, the main c++ function of the service is never called whatever the service is in the same .so or in a different .so.

However the android service called by the activity application starts.

We tried to modify the manifest with all the possibilities we found in the doc and in the forum, we are stuck.
We use Qt 5.14.(1 and 2) and android 21, 25, 28 and/or 29 and we also test Qt 5.12.7, the problem remains the same.

Typically the basic code available at https://github.com/KDAB/android/tree/master/examples/service after adapting the manifest, does not work at all with the above config.

Any help would be great !

Thanks,
Sincerely,
Thibaud.