Press twice to make an imageButton work, sometimes

As the title says, I have a simple application, with a ImageButton in the center. The fact is that by pressing the button, sometimes it does not work the first time I press it, but it works the second time. The problem occurs randomly, but always after using the menu

EDIT: I modified the MainActivity and added the xml code of the menu.

Main Activity

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

ImageButton boto;
CoordinatorLayout principal;
boolean flash;
int seleccionat;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    //Publicidad!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    AdView mAdView = (AdView) findViewById(R.id.adView);
    AdRequest adRequest = new AdRequest.Builder().build();
    mAdView.loadAd(adRequest);
    //Publicidad!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

    flash=false;
    seleccionat = 1;

    //Inicialitzacions
    boto = findViewById(R.id.imageButton);
    principal = findViewById(R.id.mainlayout);


    //Iniciem amb fons negre i botó apagat
    principal.setBackgroundResource(R.drawable.apagat_gradient_selector);
    boto.setImageResource(R.mipmap.sk0);


    boto = findViewById(R.id.imageButton);
    boto.setOnClickListener(this);

    //botó de compartir
    FloatingActionButton share = (FloatingActionButton) findViewById(R.id.share);
    share.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });
}
@Override
public void onClick(View view) {
    //canviem el boleà segons si tenim el flash engegat o apagat
    if (flash){
        flash = false;
    }else {
        flash = true;
    }
    //switch per posar diferents skins
    switch (seleccionat){
        case 1:
            //al encendre la llum posem el gradient
            if (!flash){
                boto.setImageResource(R.mipmap.sk0);
                principal.setBackgroundResource(R.drawable.apagat_gradient_selector);
            }else{
                boto.setImageResource(R.mipmap.sk1);
                principal.setBackgroundResource(R.drawable.skin1_gradient_selector);
            }
            //encenem el flash
                    /*codi per encendre flash*/
            break;
        case 2:
            //al encendre la llum posem el gradient
            if (!flash){
                boto.setImageResource(R.mipmap.sk0);
                principal.setBackgroundResource(R.drawable.apagat_gradient_selector);
            }else{
                boto.setImageResource(R.mipmap.sk2);
                principal.setBackgroundResource(R.drawable.skin2_gradient_selector);
            }
            //encenem el flash
                    /*codi per encendre flash*/
            break;
        case 3:
            //al encendre la llum posem el gradient
            if (!flash){
                boto.setImageResource(R.mipmap.sk0);
                principal.setBackgroundResource(R.drawable.apagat_gradient_selector);
            }else{
                boto.setImageResource(R.mipmap.sk3);
                principal.setBackgroundResource(R.drawable.skin3_gradient_selector);
            }
            //encenem el flash
                    /*codi per encendre flash*/
                    break;
        case 4:
            Toast.makeText(this, "Skin444", Toast.LENGTH_SHORT).show();
            break;
        case 5:
            Toast.makeText(this, "Skin555", Toast.LENGTH_SHORT).show();
            break;
        case 6:
            Toast.makeText(this, "Skin666", Toast.LENGTH_SHORT).show();
            break;
        default:
            break;
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    switch (id){
        case R.id.action_skin1:
            seleccionat = 1;
            if (!flash){
                boto.setImageResource(R.mipmap.sk0);
                principal.setBackgroundResource(R.drawable.apagat_gradient_selector);
            }else{
                boto.setImageResource(R.mipmap.sk1);
                principal.setBackgroundResource(R.drawable.skin1_gradient_selector);
            }
            break;
        case R.id.action_skin2:
            seleccionat = 2;
            if (!flash){
                boto.setImageResource(R.mipmap.sk0);
                principal.setBackgroundResource(R.drawable.apagat_gradient_selector);
            }else{
                boto.setImageResource(R.mipmap.sk2);
                principal.setBackgroundResource(R.drawable.skin2_gradient_selector);
            }
            break;
        case R.id.action_skin3:
            seleccionat = 3;
            if (!flash){
                boto.setImageResource(R.mipmap.sk0);
                principal.setBackgroundResource(R.drawable.apagat_gradient_selector);
            }else{
                boto.setImageResource(R.mipmap.sk3);
                principal.setBackgroundResource(R.drawable.skin3_gradient_selector);
            }
            break;
        case R.id.action_skin4:
            seleccionat = 4;
            Toast.makeText(this, "Skin4", Toast.LENGTH_SHORT).show();
            break;
        case R.id.action_skin5:
            seleccionat = 5;
            Toast.makeText(this, "Skin5", Toast.LENGTH_SHORT).show();
            break;
        case R.id.action_skin6:
            seleccionat = 6;
            Toast.makeText(this, "Skin6", Toast.LENGTH_SHORT).show();
            break;
        default:
            break;
    }
    return super.onOptionsItemSelected(item);
}

}

the XML

<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:theme="@style/AppTheme.AppBarOverlay"
    android:background="@android:color/transparent">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="@android:color/transparent"
        app:popupTheme="@style/AppTheme.PopupOverlay" />

</android.support.design.widget.AppBarLayout>

<ImageButton
    android:id="@+id/imageButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:background="@null"/>

<android.support.design.widget.FloatingActionButton
    android:id="@+id/share"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|end"
    android:layout_margin="@dimen/fab_margin"
    app:backgroundTint="?attr/actionModeSplitBackground"
    app:srcCompat="@android:drawable/ic_menu_share" />

<com.google.android.gms.ads.AdView
    android:id="@+id/adView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom"
    ads:adSize="BANNER"
    ads:adUnitId="@string/banner_ad_unit_id">
</com.google.android.gms.ads.AdView>

<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
tools:context="gmustudios.threshlantern.MainActivity">
<item
    android:id="@+id/action_skin1"
    android:orderInCategory="100"
    android:title="@string/Skin1"
    app:showAsAction="never" />
<item
    android:id="@+id/action_skin2"
    android:orderInCategory="100"
    android:title="@string/Skin2"
    app:showAsAction="never" />
<item
    android:id="@+id/action_skin3"
    android:orderInCategory="100"
    android:title="@string/Skin3"
    app:showAsAction="never" />
<item
    android:id="@+id/action_skin4"
    android:orderInCategory="100"
    android:title="@string/Skin4"
    app:showAsAction="never" />
<item
    android:id="@+id/action_skin5"
    android:orderInCategory="100"
    android:title="@string/Skin5"
    app:showAsAction="never" />
<item
    android:id="@+id/action_skin6"
    android:orderInCategory="100"
    android:title="@string/Skin6"
    app:showAsAction="never" />

It seems as if by using the menu, the activity will stay in the background until you click and then it works. Does anyone know where the problem might come from?