Wait what?
I haven't updated Zelda to 1.20 yet.
The Amiibo isn't maxed out any longer after the update?
Mine was not 20 hearts anymore. Not sure what of these steps actually made it work but what I did was boot up Twilight Princess make a new save with the Hardy name (which was the name it was registered to from Wolf Link (20 Hearts, Cave of Shadows Beaten, B40).bin) then re-load that and popped the tag at the save/load/copy screen in TP. Then when I went back into Breath of the Wild boom 20 hearts again. Before I made that save with the name Hardy it would only ever give me a 3 heart wolf, I was getting very frustrated lol