Designer show Preview a bit (than disappear)

Question

Not sure why, but when I open a *.xml file in the designer, it disappear after some seconds.

Some errors? I only see warnings.

Here's the whole:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/mxbg"
    android:orientation="vertical"
    android:weightSum="10"
    tools:context=".PlayerActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="7"
        android:gravity="center"
        android:orientation="vertical">
        <TextView
            android:id="@+id/txtsn"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_margin="20dp"
            android:ellipsize="marquee"
            android:padding="10dp"
            android:marqueeRepeatLimit="marquee_forever"
            android:scrollHorizontally="true"
            android:singleLine="true"
            android:text="Song Name"
            android:textAlignment="center"
            android:textColor="#fff"
            android:textSize="22sp"
            android:layout_marginBottom="20dp"
            android:textStyle="italic">

        </TextView>

        <ImageView
            android:id="@+id/imageview"
            android:layout_width="250dp"
            android:layout_height="250dp"
            android:layout_marginBottom="8dp"
            android:src="@drawable/musix">

        </ImageView>

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="60dp">

            <TextView
                android:id="@+id/txtsstart"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_toLeftOf="@+id/seekbars"
                android:layout_centerInParent="true"
                android:layout_alignParentLeft="false"
                android:layout_marginLeft="20dp"
                android:text=""
                android:textColor="#fff"
                android:textSize="14sp">

            </TextView>

            <TextView
                android:id="@+id/txtsstop"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_toRightOf="@+id/seekbars"
                android:layout_centerInParent="true"
                android:layout_alignParentRight="false"
                android:text=""
                android:textColor="#fff"
                android:textSize="14sp">

            </TextView>

            <SeekBar
                android:id="@+id/seekbars"
                android:layout_width="250dp"
                android:layout_height="wrap_content"
                android:layout_centerInParent="true"
                android:layout_alignParentBottom="true"
                android:layout_margin="20dp"
                android:layout_marginBottom="40dp">

            </SeekBar>
        </RelativeLayout>

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="3">

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:padding="5dp">

            <Button
                android:id="@+id/playbtn"
                android:layout_width="70dp"
                android:layout_height="70dp"
                android:layout_centerHorizontal="true"
                android:layout_marginTop="5dp"
                android:background="@drawable/ic_pause">

            </Button>

            <Button
                android:id="@+id/btnnext"
                android:layout_width="50dp"
                android:layout_height="50dp"
                android:layout_marginTop="15dp"
                android:layout_toRightOf="@+id/playbtn"
                android:background="@drawable/ic_next">

            </Button>

            <Button
                android:id="@+id/btnff"
                android:layout_width="40dp"
                android:layout_height="40dp"
                android:layout_marginLeft="15dp"
                android:layout_marginTop="20dp"
                android:layout_toRightOf="@+id/btnnext"
                android:background="@drawable/ic_fast_forward">

            </Button>

            <Button
                android:id="@+id/btnfr"
                android:layout_width="40dp"
                android:layout_height="40dp"
                android:layout_marginTop="20dp"
                android:layout_marginRight="15dp"
                android:layout_toLeftOf="@+id/btnprev"
                android:background="@drawable/ic_fast_rewind">

            </Button>

            <Button
                android:id="@+id/btnprev"
                android:layout_width="50dp"
                android:layout_height="50dp"
                android:layout_marginTop="15dp"
                android:layout_toLeftOf="@+id/playbtn"
                android:background="@drawable/ic_prev">

            </Button>

            <com.gauravk.audiovisualizer.visualizer.BarVisualizer xmlns:custom="http://schemas.android.com/apk/res-auto"
                android:id="@+id/bar"
                android:layout_width="match_parent"
                android:layout_height="70dp"
                android:layout_alignParentBottom="true"
                custom:avColor="#FF362E"
                custom:avDensity="0.5"
                custom:avSpeed="normal"
                custom:avType="outline"
                custom:avWidth="4dp" />

        </RelativeLayout>

    </LinearLayout>

</LinearLayout>

Which result in this:

What's wrong?