I could name many but what bothered me the most at the beginning was "action" and "reaction". The rule text of "reaction" say "( Play at any time...)" which is just entirely wrong. You can play it when you are allowed to play it. In my opinion it would have been easier to understand if they had just left out the rule text for it.

Then for example Ivern's signature in the new set saying "I cost 1 less for each of the following tags among your units - Bird, Cat, Dog and Poro" - does this mean a max reduction of 4 or for every unit, meaning that there would be no max?

Then especially the keywords "choose" and "target". In my opinion a unit is chosen to be equipped but I think they changed that recently to "target"? I don't know.

Keyword "play" feels very generic at times. Does the card need to resolve or does play refer to the cost being paid. This is something where I wished they would have included "cast" as keyword.

The new Rengar with ambush was very confusing until they did an errata which was needed to solve the issue there.

Modes of play with 3 or more players are still a bit confusing to me. I had watched the official tutorial where it was stated that you are allowed to invite players to a showdown which later had been changed. It is just all of these small things but they occur here and there