• App starts fine.
• Put app in background, e.g. home button, app switcher, whatever.
• Bring app back to foreground and observe, either
  a) screen goes black and stays black
  or b) screen shows image from previous app, because my app is not drawing.

log shows:
Window has been abandoned! return value -19
QEGLPlatformContext: eglMakeCurrent failed: 300b (EGL_BAD_NATIVE_WINDOW)

Similar to QTBUG-45019, but a fix for that went in on 5.5.0 beta and I'm having this issue on 5.5.1, but only with a particular device/config that my client has.

more log below...
I/System.out( 5624): onResume
D/KeyguardUpdateMonitor( 742): sendKeyguardVisibilityChanged(true)
I/KeyguardUpdateMonitor( 742): visibility is same
I/RiffTrax( 5624): app state: active
D/PointerIcon( 570): setMouseIconStyle1 pointerType: 1001iconType:101 flag:0
D/PointerIcon( 570): setMouseCustomIcon IconType is same.101
D/PhoneStatusBar( 742): setSemiTransparentMode=false, mTransparentMode=false, mSemiTransparentMode=false, mMultiWindowMode=false
E/BufferQueue( 142): [SurfaceView] query: BufferQueue has been abandoned!
E/ ( 5624): Window has been abandoned! return value -19
E/libEGL ( 5624): eglMakeCurrent:779 error 300b (EGL_BAD_NATIVE_WINDOW)
W/libRiffTrax.so( 5624): (null):0 ((null)): QEGLPlatformContext: eglMakeCurrent failed: 300b
E/libEGL ( 5624): call to OpenGL ES API with no current context (logged once per thread)
E/BufferQueue( 142): [SurfaceView] query: BufferQueue has been abandoned!
E/ ( 5624): Window has been abandoned! return value -19
E/libEGL ( 5624): eglMakeCurrent:779 error 300b (EGL_BAD_NATIVE_WINDOW)
W/libRiffTrax.so( 5624): (null):0 ((null)): QEGLPlatformContext: eglMakeCurrent failed: 300b
D/QtPositioning( 5624): Looper Thread startup time in ms: 1