corrected using Vi0L0's solution.what seemed to be happening is that xnconvert loads its own libqxcb.so which loads /usr/lib/libfontconfig.so but then loads the provided libfreetype.so.6 instead of the system's one. However the provided libfreetype.so.6 is not compatible with the system's one. The solution is to remove the provided libfreetype.so.6.