It’s a problem with the level-up guestimation algorithm – or, more accurately, a lack of available data.
- In most cases, it’s able to use your Radical unlock dates, and that’s the most accurate.
- When a level doesn’t have radicals, it has to drop back to using the Kanji unlock dates. But you haven’t done any kanji lessons on your current level, so it can’t use that either.
- When it can’t use the current-level kanji, it tries to guess based on your previous level’s vocabulary unlock dates. But you’ve only done two vocab lessons from your previous level, so that fails, too.
- Finally, it just returns zero as your level-up time, which is Jan 1, 1970.
Anyway, it will be retroactively fixed once you start doing kanji lessons on your current level.
In my spare time, I’m updating wkstats.com to use APIv2, which does provide the level-up date explicitly. When that’s done, this kind of problem will mostly go away (except for old level-ups from before Wanikani started tracking level-up dates).