[Arm NN on Cortex-A9] Static build leads to "None of the preferred backends [CpuRef ] are supported" error at runtime

Hello ArmNN experts,
I'm currently facing an issue at runtime when using a statically built ArmNN lib.

I have been able to build a STATIC version of libarmnn with all dependancies and then build my own app for a Wandboard target (armv7).
At runtime I got this error: "ERROR: None of the preferred backends [CpuRef ] are supported. Current platform provides []"

When I compile SHARED libraries (*.so) the exact same app is running fine, and the inference is done as expected.

ArmNN version: 21.02
Model/Target: TFLite on armv7
Build options: cmake .. -DCMAKE_LINKER=/usr/bin/arm-linux-gnueabihf-ld -DCMAKE_C_COMPILER=/usr/bin/arm-linux-gnueabihf-gcc -DCMAKE_CXX_COMPILER=/usr/bin/arm-linux-gnueabihf-g++ -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_STANDARD=14 -DCMAKE_CXX_FLAGS=-mfpu=neon -DARMCOMPUTE_ROOT=$BASEDIR/ComputeLibrary -DARMCOMPUTE_BUILD_DIR=$BASEDIR/ComputeLibrary/build -DBOOST_ROOT=$BASEDIR/boost_1_64_0 -DTF_GENERATED_SOURCES=$BASEDIR/tensorflow-protobuf -DBUILD_TF_PARSER=0 -DBUILD_ONNX_PARSER=0 -DONNX_GENERATED_SOURCES=$BASEDIR/onnx -DBUILD_TF_LITE_PARSER=1 -DTF_LITE_GENERATED_PATH=$BASEDIR/tflite -DFLATBUFFERS_ROOT=$BASEDIR/flatbuffers-arm32 -DFLATC_DIR=$BASEDIR/flatbuffers/build -DPROTOBUF_ROOT=$BASEDIR/protobuf-arm -DARMCOMPUTENEON=1 -DARMNNREF=1

Does anyone have an idea of a fix or additionnal investigations ??
Thanks!!

Regards,
Nicolas