I have tested with VirusTotal an older version of my app and it doesn't report the HiddenAds infection.
So I have continued to upload all the newer versions to see where this issue start and it is between version 2.07 to 2.08.
In the code there is just a bug fix in 2.08, but looking to AndroidManifest.xml I see a difference:
This is 2.07 without infection
<service android:name="com.google.firebase.components.ComponentDiscoveryService" >
<meta-data
android:name="com.google.firebase.components:com.google.firebase.analytics.connector.internal.AnalyticsConnectorRegistrar"
android:value="com.google.firebase.components.ComponentRegistrar" />
<meta-data
android:name="com.google.firebase.components:com.google.firebase.iid.Registrar"
android:value="com.google.firebase.components.ComponentRegistrar" />
</service>
and this is 2.08 with infection
<service android:name="com.google.firebase.components.ComponentDiscoveryService" >
<meta-data
android:name="com.google.firebase.components:com.google.firebase.analytics.connector.internal.AnalyticsConnectorRegistrar"
android:value="com.google.firebase.components.ComponentRegistrar" />
<meta-data
android:name="com.google.firebase.components:com.google.firebase.iid.Registrar"
android:value="com.google.firebase.components.ComponentRegistrar" />
<meta-data
android:name="com.google.firebase.components:com.google.firebase.auth.FirebaseAuthRegistrar"
android:value="com.google.firebase.components.ComponentRegistrar" />
</service>
The text in the Manifest editor is identical between the two versions.
I don't know if this can be of interest to experts.
Edit: vs 2.07 was compiled on 29 Jun 2018, while 2.08 on 02 Nov 2018. Probably with some different library version or B4A version