There is currently no way to cancel Wuclone beside running into a nullifier or getting it killed.
When having "Celestial Stomp" augument equipped. As it overwrites the unsummon command.
Its not that major issue but sometimes Wuclone gets stuck and doesn't teleport back to you or fails to even use the slam at all or is stuck with melee only or not using weapons at all (Happens sometimes)
Only way to fix these is to resummon the Wuclone which is not possible to do anymore while us