Android App not starting - Only on Galaxy S4

Android App not starting - Only on Galaxy S4

I'm developing a game on Android that has been running well over months on
all devices I know of. But recently I noticed that S4 users typically
uninstall the app right away, and finally someone with an S4 (jflte) wrote
a review, stating that the app "does not start".
I cannot reproduce this behaviour in an AVD (related) and won't have an S4
at hand any time soon. Googling the issue, I found that this is not
umcommon with S4's and might be related to SD-card installs. I did not
find any solution though. My app uses OpenGL with
android.opengl.GLSurfaceView.
Question is: What are my options to investigate the problem? I've seen the
RTL option, but it seems to be some kind of premium thing. I would love to
have LogCat output of the startup attempts on an S4.
Here's my AndroidManifest, as far as relevant:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="app.orbs"
android:versionCode="24"
android:versionName="2.1"
android:installLocation="auto" >
<uses-sdk
android:minSdkVersion="7"
android:targetSdkVersion="18" />
<application
android:allowBackup="true"
android:icon="@drawable/orb_launcher"
android:label="@string/app_name"
android:name="orbs.OrbsApplication">
<activity
android:name="orbs.controller.MainMenuActivity"
android:screenOrientation="portrait"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="orbs.controller.GameActivity"
android:screenOrientation="portrait"
android:label="@string/app_name" >
</activity>
<activity
android:name="orbs.SettingsActivity"
android:label="@string/app_name"
android:theme="@android:style/Theme.NoTitleBar" >
<intent-filter>
<category android:name="android.intent.category.PREFERENCE" />
</intent-filter>
</activity>
</application>
Thanks in advance!