Open App on 2 different Devices at the same Time

I am trying to automate a TestCase on multiple devices, running them in Threads. Everything is working fine, but when i am trying to Launch an App, it works on one Device but not on the other Device.

My Setup:
DesiredCapabilities caps = new DesiredCapabilities();
caps.setCapability(“deviceName”, deviceName);
caps.setCapability(“app”, “C:\Appium\Appium\node_modules\appium\build\unlock_apk\unlock_apk-debug.apk”);

    caps.setCapability("appPackage", "Package");

    driverUrl =   "" + getPort() + "/wd/hub";
    driver = new AndroidDriver(new URL(driverUrl), caps);

It works with e.g. Youtube , but not when i try to open my own APPLICATION. Then it only starts on my SAMSUNG GALAXY S7 not on the S4. Someone knows why?

All the Parameters like DeviceName etc. ist given the class in the Main, so it is no Code Problem. pressing Button works on both Devices . Only launching App isn’t working. I can also put my whole Code, if needed.

Thanks, if someone can help me.