XML : Android Studio: Application works fine in emulator, but missing body on real phone?

I've run my app on the Android Studio emulator and it works just fine. However, when I ran it on my real phone, all the MainActivity buttons were missing. I don't know exactly what caused it, but I don't suspect it's my Java classes since they weren't even activated, and commenting them out (leaving only the layout xmls) doesn't fix it. I suspect it's something I messed up with the Gradle or manifest files. Here they are:

app gradle:

  apply plugin: 'com.android.application'    android {      compileSdkVersion 23      buildToolsVersion "23.0.1"        defaultConfig {          applicationId "com.johan.AppName"          minSdkVersion 15          targetSdkVersion 23          versionCode 1          versionName "1.0"      }      buildTypes {          release {              minifyEnabled false              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'          }      }      sourceSets { main { assets.srcDirs = ['src/main/assets', 'src/main/assets/'] } }  }    dependencies {      compile fileTree(include: ['*.jar'], dir: 'libs')      compile 'com.android.support:appcompat-v7:23.1.1'      compile files('libs/exp4j-0.4.5.jar')  }    

AppName gradle file:

  // Top-level build file where you can add configuration options common to all sub-projects/modules.    buildscript {      repositories {          jcenter()      }      dependencies {          classpath 'com.android.tools.build:gradle:1.3.0'            // NOTE: Do not place your application dependencies here; they belong          // in the individual module build.gradle files      }  }    allprojects {      repositories {          jcenter()      }  }    

AndroidManifest.xml:

  <?xml version="1.0" encoding="utf-8"?>  <manifest xmlns:android="http://schemas.android.com/apk/res/android"            package="com.johan.AppName">        <application          android:allowBackup="true"          android:icon="@mipmap/ic_launcher"          android:label="@string/app_name"          android:fullBackupContent="false"          android:theme="@style/AppTheme">          <activity              android:name=".MainActivity"              android:label="@string/app_name">              <intent-filter>                  <action android:name="android.intent.action.MAIN"/>                    <category android:name="android.intent.category.LAUNCHER"/>              </intent-filter>          </activity>      </application>  </manifest>    

When I run the app on my phone through Android Studio using a non-debug mode, I get the following warnings:

  01-15 19:29:43.327  29144-29144/com.johan.AppName W/dalvikvm﹕ VFY: unable to find class referenced in signature (Landroid/view/SearchEvent;)  01-15 19:29:43.327  29144-29144/com.johan.AppName W/dalvikvm﹕ VFY: unable to resolve interface method 14825: Landroid/view/Window$Callback;.onSearchRequested (Landroid/view/SearchEvent;)Z  01-15 19:29:43.327  29144-29144/com.johan.AppName W/dalvikvm﹕ VFY: unable to resolve interface method 14829: Landroid/view/Window$Callback;.onWindowStartingActionMode (Landroid/view/ActionMode$Callback;I)Landroid/view/ActionMode;  01-15 19:29:43.777  29144-29144/com.johan.AppName W/dalvikvm﹕ VFY: unable to resolve virtual method 535: Landroid/content/res/TypedArray;.getChangingConfigurations ()I  01-15 19:29:43.777  29144-29144/com.johan.AppName W/dalvikvm﹕ VFY: unable to resolve virtual method 557: Landroid/content/res/TypedArray;.getType (I)I    

I tried googling these warnings, but the only solutions that came about were relating to working under Eclipse.

My phone is a Samsung Galaxy Grand 2 running Android 4.3, I have previously managed to successfully run the application on my phone before, I have absolutely no clue on what to do.