I got exactly the same problem when I tried to use Mayflash adapater+Wii U pro controller on Nintendont.
But there is no probem at all if I use them on my PC with Dolphin.
So I think the problem is currently "Mayflash adapater+Wii U pro controller"
is not compatible with Nintendont.
not true the Mayflash adapter+Wii U pro controller works fine for me