Hi,
It looks like you install a package for python2.7 rather than python3:
sudo pip install mxnet-1.4.0-cp27-cp27mu-linux_aarch64.whl
A typical segmentation fault is caused by the incompatibility of a package or library.
It is recommended to check if the package provided by the mxnet team was not built on JetPack4.3 or not.
We also have a mxnet package for JetPack4.3.
You can find more information here:
Thanks.