Android app runs on Cortex A9 processor but not on Cortex A7

My Android app, which uses a C++ library built using the NDK, runs on a Nexus 7 (Android 4.3, processor = ARM Cortex A9), and on another tablet using Android 6.1, but fails on two other devices using the ARM Cortex A7 processor.

One of the failing devices is a mobile phone running Android 5.1 (symptom of failure = black screen on startup, and no subsequent progress).

The other failing device is a development board (http://ift.tt/296sN1I), on which the symptom of failure is the normal 'unfortunately app has stopped' message.

I don't think the problem is lack of RAM in the case of the development board; it has 1GB of RAM, which is the same as that of the Nexus 7.

The C++ library is built using C++11: the android.mk file includes the lines

LOCAL_CPP_FEATURES=exceptions
LOCAL_CPPFLAGS += -std=c++11

and the application.mk file is

APP_ABI := armeabi x86
APP_STL := c++_static

I can't find any reference to this problem anywhere on the web.