This is something I’ve been noticing lately, and I’m not sure if it’s real or if my brain is lying to me…
I swear that when I do my lessons, sometimes (or maybe always?) it doesn’t actually quiz me on each item. For example, I just did 10 vocabulary lessons in two batches of 5, and for each batch of 5 I only wrote nine answers… I think. I keep meaning to write these down as I go so that I can be sure, but I keep forgetting to actually do it 
But I swear that in the last batch I did, I had 各自 come up and I answered the reading… but then I don’t believe I ever got prompted to answer the meaning. I was anticipating it and I don’t think I ever saw it come up. And I could swear I’ve had a bunch of these as of late! It’s just a bit hard to keep track of and say definitively since they come in a random order. Has anyone else noticed this??
I’m unsure if it happens in normal review sessions as well. I sort of feel like it did today, but I’m not quite sure… hopefully me making this post will remind me next time to pay closer attention to it and make sure I get prompted for all parts of all items. I could swear there’s stuff slipping through the cracks here, but it’s really subtle.
(I use WaniKani completely vanilla, no userscripts or third party apps that could be interfering)