Good morning, thank you all for the suggestions! I found out that the antivirus reporting the false positive is Avast (installed by default on all Huawei devices).
I sent a report to the Avast team: they immediately removed my app from their virus database, but in the meantime a lot of users uninstalled the app and gave bad reviews.
From now on, before publishing the app, I will first send the APK of the app in the form "False positives" Avast.