Animation recyclerView crash to android 4

делаю Animation recyclerView....на андроидах 5,6,7 все работает, а на 4 нет....помогите разобраться...

public class PostAdapter extends RecyclerView.Adapter<PostAdapter.PostViewHolder>{
    @Override
    public void onBindViewHolder(final PostViewHolder holder, final int position) {
        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(ctx);
        boolean checkBox = prefs.getBoolean("chb3", true);
        if(checkBox == true){
        if(position >lastPosition) {
            Animation animation = AnimationUtils.loadAnimation(ctx,
                    R.anim.up_from_bottom);
            holder.itemView.startAnimation(animation);
            lastPosition = position;
        }else {
            if(checkBox == false){
                if(position >lastPosition) {
                    Animation animation = AnimationUtils.loadAnimation(ctx,
                            R.anim.up_from_bottom);
                    holder.itemView.startAnimation(null);
                    lastPosition = position;
        }}}}

ошибка такая

android.support.v4.app.FragmentManagerImpl.checkStateLoss (FragmentManager.java:1832)
android.support.v4.app.FragmentManagerImpl.popBackStackImmediate (FragmentManager.java:774)
android.support.v4.app.FragmentActivity.onBackPressed (FragmentActivity.java:178)
android.app.Activity.onKeyUp (Activity.java:2718)
android.view.KeyEvent.dispatch (KeyEvent.java:3224)
android.app.Activity.dispatchKeyEvent (Activity.java:2986)
android.support.v7.app.AppCompatActivity.dispatchKeyEvent (AppCompatActivity.java:543)
android.support.v7.view.WindowCallbackWrapper.dispatchKeyEvent (WindowCallbackWrapper.java:53)
android.support.v7.app.AppCompatDelegateImplBase$AppCompatWindowCallbackBase.dispatchKeyEvent (AppCompatDelegateImplBase.java:312)
android.support.v7.view.WindowCallbackWrapper.dispatchKeyEvent (WindowCallbackWrapper.java:53)
com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent (PhoneWindow.java:2613)
android.view.ViewRootImpl$ViewPostImeInputStage.processKeyEvent (ViewRootImpl.java:4942)
android.view.ViewRootImpl$ViewPostImeInputStage.onProcess (ViewRootImpl.java:4897)
android.view.ViewRootImpl$InputStage.deliver (ViewRootImpl.java:4361)
android.view.ViewRootImpl$InputStage.onDeliverToNext (ViewRootImpl.java:4414)
android.view.ViewRootImpl$InputStage.forward (ViewRootImpl.java:4380)
android.view.ViewRootImpl$AsyncInputStage.forward (ViewRootImpl.java:4506)
android.view.ViewRootImpl$InputStage.apply (ViewRootImpl.java:4388)
android.view.ViewRootImpl$AsyncInputStage.apply (ViewRootImpl.java:4563)
android.view.ViewRootImpl$InputStage.deliver (ViewRootImpl.java:4361)
android.view.ViewRootImpl$InputStage.onDeliverToNext (ViewRootImpl.java:4414)
android.view.ViewRootImpl$InputStage.forward (ViewRootImpl.java:4380)
android.view.ViewRootImpl$InputStage.apply (ViewRootImpl.java:4388)
android.view.ViewRootImpl$InputStage.deliver (ViewRootImpl.java:4361)
android.view.ViewRootImpl$InputStage.onDeliverToNext (ViewRootImpl.java:4414)
android.view.ViewRootImpl$InputStage.forward (ViewRootImpl.java:4380)
android.view.ViewRootImpl$AsyncInputStage.forward (ViewRootImpl.java:4539)
android.view.ViewRootImpl$ImeInputStage.onFinishedInputEvent (ViewRootImpl.java:4781)
android.view.inputmethod.InputMethodManager$PendingEvent.run (InputMethodManager.java:2828)
android.view.inputmethod.InputMethodManager.invokeFinishedInputEventCallback (InputMethodManager.java:2416)
android.view.inputmethod.InputMethodManager.finishedInputEvent (InputMethodManager.java:2407)
android.view.inputmethod.InputMethodManager$ImeInputEventSender.onInputEventFinished (InputMethodManager.java:2805)
android.view.InputEventSender.dispatchInputEventFinished (InputEventSender.java:141)
android.os.MessageQueue.nativePollOnce (MessageQueue.java)
android.os.MessageQueue.next (MessageQueue.java:143)
android.os.Looper.loop (Looper.java:130)
android.app.ActivityThread.main (ActivityThread.java:6917)
java.lang.reflect.Method.invoke (Method.java)
java.lang.reflect.Method.invoke (Method.java:372)
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run (ZygoteInit.java:1404)
com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1199)