Have you tried to do what the guide suggest? I literally just did this twice in a row on a N3DS and an O3DS. It clearly states and I'm paraphrasing here, "(PLai)sysUpdater WILL freeze at HAX Init when using secondary exploits such as SMHaxx, Bashaxx, etc. The fix this you have to load a HomeBrew (Any HomeBrew) and return to the HomeBrew menu without exiting. THEN run the sysupdater to downgrade".
EDIT: "If you are using supermysterychunkhax or smashbroshax as your entrypoint, you should open any homebrew application (such as menuhax_manager) then close it back to the Homebrew Launcher (which will fix memory contents). If you do not, svchax will not init properly."