Why doesn't Android Studio see JNI functions?

Question

Java

Android Studio does not see JNI functions.
error:"Cannot resolve corresponding JNI function..."

build.gradle:

apply plugin: 'com.android.application'
android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.example.m.f"
        minSdkVersion 15
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags "-frtti -fexceptions"
            }
        }
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
    sourceSets { main { jni.srcDirs = ['src/main/jni', 'src/main/jni/jniLibs'] } }
}

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    implementation project(':openCVLibrary342dev')
}

face.java

... 
// C++:  Ptr_Facemark cv::face::createFacemarkAAM()
    private static native long createFacemarkAAM_0();

    // C++:  Ptr_Facemark cv::face::createFacemarkKazemi()
    private static native long createFacemarkKazemi_0();

    // C++:  Ptr_Facemark cv::face::createFacemarkLBF()
    private static native long createFacemarkLBF_0();
...

The function definition is in the *.so file.
The file is added to the jniLibs folder.