Android I only change applicationId in gradle and the bug fixed. But I don't know why?

I develop an application with BLE API. Firstly, the function startScan() didn't work. But when I change the variable of applicationId in Gradle, the code works well. I cannot understand why? Can anyone give me an answer? :D

Old version:

defaultConfig {
        applicationId "com.example.facemask"
        minSdkVersion 27
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

New version:

defaultConfig {
        applicationId "com.example.displaydata"
        minSdkVersion 27
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }