Greasy Fork is available in English.
This UserScript is a descendant of the WaniKani Customizer Chrome Extension Timeline
Strange. I just burned one item, and now the timeline is accurate. I had refreshed a second tab in the middle of reviewing my current level radicals/kanji, so the incomplete timeline was probably generated at that time, but it never updated as I refreshed the tab/opened new ones.
The timeline will only update if it has been more than one-hour since the last time it updated, otherwise it just loads cached data. This is to avoid sending too many WK api requests. Perhaps this is causing the behavior you are noticing.
That is sensible, but it needs to do a forced update at the end of each review session or lesson to prevent this sort of thing. Perhaps a manual update option?
A force/manual update button has been added.
Look for the 'R' (for reload) button on the top line.
Current Level Radicals/Kanji Dissapearing
My current level radicals are in three bunches tomorrow morning. 1 radical + 1 vocab at 7:45, 4 radicals + 5 kanji + 5 vocab at 8:00, 3 radicals + 1 kanji + 3 vocab at 8:15. My timeline only shows 1 radical at 7:45 and then nothing else until 10:00. My current level kanji have a similar problem. This is on desktop Firefox with Greasemonkey on Windows XP.