Yeah, when I first got to that point I quickly realized you have to get to the critical point where you can read native content ASAP otherwise the knowledge slowly leaks out. I’ve seen lvl 60s acknowledge this as well elsewhere in the forums.
I’m sure you already know, but for me the bookclubs: Master List of Book Clubs?
and one of the Burn Managers/Self Study quizzes: [Userscript] Self-Study Quiz? work really well for going over these things. For the latter, you can filter by level and do an organized review that way if you want.
That’s the best part of Wanikani for me: all the things the community has made to help each other out.