I think either the RNG is bugged, or the game is programmed to alter odds depending on factors unknown to us. For example:
Season 1.3: I’ve purchased 75 ultimate caches, and still haven’t gotten Oberon’s Keybelt.
Season 1.4: I got the Duskside Helmet after opening 15 ultimate caches
Season 1.5: I got the Dragonrealm Ring after opening 5 ultimate caches, around 7 basic caches, and around 5 enhanced caches.
So, I honestly have NO IDEA what to think about the RNG for this game, LOL. Yes I know the saying that “RNG will be RNG”, but the chances of NOT getting Oberon’s after opening 75 ultimate caches is something like 2%.