Android: Crash report ClassNotFoundException occurs (rarely) after every app update? Security issue?

I got a weird crash report (ClassNotFoundException) that happens after every update of my application. It looks like it has something to do with replacing the app in memory during the update, as it only happens when the update is released and many people download it (although this rarely happens), after a few days it always disappears and basically never happens ...

I suspect there is a proguard that disables some classes - but how do I know which classes are causing the problem? There is no useful information in the stack trace ... And I don't want to stop using ProGuard.

This is the stack trace:

java.lang.RuntimeException: 
  at android.app.LoadedApk.makeApplication(LoadedApk.java:572)
  at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4837)
  at android.app.ActivityThread.access$1500(ActivityThread.java:178)
  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1531)
  at android.os.Handler.dispatchMessage(Handler.java:111)
  at android.os.Looper.loop(Looper.java:194)
  at android.app.ActivityThread.main(ActivityThread.java:5643)
  at java.lang.reflect.Method.invoke(Method.java:0)
  at java.lang.reflect.Method.invoke(Method.java:372)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.ClassNotFoundException: 
  at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:469)
  at android.app.Instrumentation.newApplication(Instrumentation.java:985)
  at android.app.LoadedApk.makeApplication(LoadedApk.java:567)

      

        
        
        
      

    

EDIT: My proguard file:

-renamesourcefileattribute SourceFile
-keepattributes Exceptions,InnerClasses,Signature,Deprecated,SourceFile,LineNumberTable,*Annotation*,EnclosingMethod
-keep class org.acra.* {
    *;
}