I have been playing Hunter on Zeth'kur since release and I can confirm I have had MANY instances where my Tame Beast "Failed", at the end of the cast nothing happens and you have to start casting again... I don't know if this is intended or some serious bug as I never played hunter on retail vanilla. I also have deleted my WDB Folder and am playing on a completely fresh install of 1.12.
If anyone else has an Idea as to why Tame Beast is "Failing" so often please respond!
P.S. Sorry to hear about the other hunter, that sucks. You will get Lupos soon, keep at it.