Unity Anroid integrated into a different Android app is crashing on Application.Quit()

After we exported the project to an Android project, we integrated it with an existing project from which we're launching our game. This was working correctly, but Application.Quit() was making the entire app quit instead of just the Unity activity. So we made it launch on a different process by adding this to the manifest:

 android:process=":UnityKillsMe"

This solved the issue, however, after using Proguard to obfuscate the code, things stopped working. Unity still launches correctly, however when quitting, the app shows a crash error that Unity stopped, even though the app itself is still working. Relaunching Unity even works correctly, but on Application.Quit(), the crash error still shows. Here's the error log when it happens:

 12-02 15:01:35.112: E/AndroidRuntime(4342): FATAL EXCEPTION: UnityMain
 12-02 15:01:35.112: E/AndroidRuntime(4342): Process: mobi.foo.touch:UnityKillsMe, PID: 4342
 12-02 15:01:35.112: E/AndroidRuntime(4342): java.lang.Error: FATAL EXCEPTION [UnityMain]
 12-02 15:01:35.112: E/AndroidRuntime(4342): Unity version     : 5.2.3f1
 12-02 15:01:35.112: E/AndroidRuntime(4342):  at com.unity3d.player.UnityPlayer.nativeDone(Native Method)
 12-02 15:01:35.112: E/AndroidRuntime(4342):  at com.unity3d.player.UnityPlayer.f(Unknown Source)
 12-02 15:01:35.112: E/AndroidRuntime(4342):  at com.unity3d.player.UnityPlayer.g(Unknown Source)
 12-02 15:01:35.112: E/AndroidRuntime(4342):  at com.unity3d.player.UnityPlayer$15.run(Unknown Source)
 12-02 15:01:35.112: E/AndroidRuntime(4342):  at com.unity3d.player.UnityPlayer.executeGLThreadJobs(Unknown Source)
 12-02 15:01:35.112: E/AndroidRuntime(4342):  at com.unity3d.player.UnityPlayer$b.run(Unknown Source)
 12-02 15:01:35.122: E/ActivityManager(890): App crashed! Process: mobi.foo.touch:UnityKillsMe

How can this be solved? What's causing this issue?