Have you tried to remove setuid from flatpak-bwrap?
[nemo@GalaxyNote4 ~]$ flatpak-runner org.kde.mobile.angelfish Starting: org.kde.mobile.angelfish [D] unknown:0 - Using Wayland-EGL library "libgui.so" wasn't loaded and RTLD_NOLOAD prevented it Wayland socket: ../../display/wayland-1 WAYLAND_DISPLAY="../../display/wayland-1" FLATPAK_MALIIT_CONTAINER_DBUS="unix:abstract=/tmp/dbus-2jgsVazrhw,guid=6dbb0b460b76ace39f6f63685f2d0ab1" flatpak run --env=QT_WAYLAND_FORCE_DPI=517 --filesystem=/system:ro --filesystem=/vendor:ro --device=all --talk-name=org.maliit.server --env=QTWEBENGINE_CHROMIUM_FLAGS=--disable-gpu-compositing --num-raster-threads=1 --enable-viewport --disable-composited-antialiasing --env=QTWEBENGINE_DISABLE_GPU_THREAD=1 --env=QT_QUICK_CONTROLS_MOBILE=1 --env=QT_QUICK_CONTROLS_STYLE=Plasma --env=HYBRIS_EGLPLATFORM_DIR=/usr/lib/arm-linux-gnueabihf/GL/host/lib/libhybris --env=HYBRIS_LINKER_DIR=/usr/lib/arm-linux-gnueabihf/GL/host/lib/libhybris/linker --env=HYBRIS_LD_LIBRARY_PATH=/usr/lib/arm-linux-gnueabihf/GL/host/libexec/droid-hybris/system/lib:/usr/libexec/droid-hybris/system/lib:/vendor/lib:/system/lib --env=LD_LIBRARY_PATH=/usr/lib/arm-linux-gnueabihf/GL/host/lib org.kde.mobile.angelfish [D] onCompleted:424 - Warning: specifying an object instance for initialPage is sub-optimal - prefer to use a Component [W] unknown:53 - file:///usr/share/flatpak-runner/qml/main.qml:53:26: Unable to assign [undefined] to bool bwrap: Creating new namespace failed, likely because the kernel does not support user namespaces. bwrap must be installed setuid on such systems.
[nemo@GalaxyNote4 ~]$ flatpak-runner org.kde.mobile.angelfish Starting: org.kde.mobile.angelfish [D] unknown:0 - Using Wayland-EGL library "libgui.so" wasn't loaded and RTLD_NOLOAD prevented it Wayland socket: ../../display/wayland-2 WAYLAND_DISPLAY="../../display/wayland-2" FLATPAK_MALIIT_CONTAINER_DBUS="unix:abstract=/tmp/dbus-1MAKn0UhdE,guid=ff1e7aa17d091e23d6b5f2775f2d0bb5" flatpak run --env=QT_WAYLAND_FORCE_DPI=517 --filesystem=/system:ro --filesystem=/vendor:ro --device=all --talk-name=org.maliit.server --env=QTWEBENGINE_CHROMIUM_FLAGS=--disable-gpu-compositing --num-raster-threads=1 --enable-viewport --disable-composited-antialiasing --env=QTWEBENGINE_DISABLE_GPU_THREAD=1 --env=QT_QUICK_CONTROLS_MOBILE=1 --env=QT_QUICK_CONTROLS_STYLE=Plasma --env=HYBRIS_EGLPLATFORM_DIR=/usr/lib/arm-linux-gnueabihf/GL/host/lib/libhybris --env=HYBRIS_LINKER_DIR=/usr/lib/arm-linux-gnueabihf/GL/host/lib/libhybris/linker --env=HYBRIS_LD_LIBRARY_PATH=/usr/lib/arm-linux-gnueabihf/GL/host/libexec/droid-hybris/system/lib:/usr/libexec/droid-hybris/system/lib:/vendor/lib:/system/lib --env=LD_LIBRARY_PATH=/usr/lib/arm-linux-gnueabihf/GL/host/lib org.kde.mobile.angelfish [D] onCompleted:424 - Warning: specifying an object instance for initialPage is sub-optimal - prefer to use a Component [W] unknown:53 - file:///usr/share/flatpak-runner/qml/main.qml:53:26: Unable to assign [undefined] to bool bwrap: execvp xdg-dbus-proxy: No such file or directory