Angle between two 3D vectors in degrees

My goal is to rotate the enemies in my game to look towards my player. The code for it looks like this:

struct Entity {
    glm::vec3 Position;
    glm::vec3 Scale;
    glm::vec3 Rotation;
};

void turnEnemies() {
// the direction all ships look towards when spawned
    glm::vec3 defaultShipForward = glm::vec3( 0.0f, 0.0f, 1.0f );

    std::vector<Entity*> ships = ...;

    for (int i = 0; i < ships.size(); i++) {
        Entity* curShip = ships[i];
        if (curShip == m_player) continue;

// I only rotate the ships around the y-axis. 
// So I create a rotation matrix to rotate the ships default forward vector towards it's actual one
        glm::mat4 rotationMat = glm::rotate( glm::mat4( 1.0f ), curShip->Rotation.y, 
        glm::vec3( 0.0f, 1.0f, 0.0f ) );
        glm::vec3 curShipForward =  glm::normalize(rotationMat * glm::vec4(defaultShipForward, 1.0f));

// get the vector from the current ships position toward the player
        glm::vec3 vecToPlayer = glm::normalize( m_player->Position - ships[i]->Position );

        float turnAngle = getAngleBetweenVectorsDeg( curShipForward, vecToPlayer );

        ships[i]->Rotation.y += turnAngle;
    }
}

I implemented the following variants I found online for calculating the angle:

float getAngleBetweenVectorsDeg( glm::vec3 _vec1, glm::vec3 _vec2 ) {
    return acos( glm::dot( _vec1, _vec2 ) );
}

float getAngleBetweenVectorsDeg( glm::vec3 _vec1, glm::vec3 _vec2 ) {
    return  atan2( glm::length( glm::cross( _vec1, _vec2 ) ), glm::dot( _vec1, _vec2 ) );
}

With the acos solution, the rotation becomes undefined. The atan results in weird rotations, where one enemy rotates when the player moves forwards, the other when he moves backwards.