I noticed that my Xoris could hardly gain combo points when being throwed.
Then I tried Glaive Prime, Falcor, and un-modded Xoris in Simulacrum.
My conclusion is that, I should throw galives after jumping up or during falling, to let them gain combo points when being throwed.
If I just stand on the ground and throw, no combo point is added.
This is a bug, I think.