WaniKani, like any learning system, is simply a tool to help you find your way. The purpose is to teach you HOW to learn, how to cement all these kanji/vocab to memory, and create personal tags of your own. Take the mnemonics for instance… as you go further along you will see the very same mnemonics used for very very similiar kanji. Why is that? Because it’s a suggestion of a method and it’s up to you to determine what will work best for you.
Even the list of similiar kanji isn’t set in stone. It’s only a generalization. Frankly I didn’t even notice how simliar those two kanji are until you pointed it out! 差別 takes place at a construction site with a buzz saw さ in my memory palace and 着々 is one of many vocab that takes place at a party with plenty of different clothes and a steady stream of people arriving and leaving eating mochi that taste like chalk ちゃく
Listen, I’ve been there…albeit I ran into this problem ten levels later on…but since this is hitting you now, maybe that’s a good thing! Maybe I can save you the pain before bad habits of just “following along” start to set fester instead of carving what is best for you from the ground up!