Wrong word strength
The Vocabulary section is way off.
Out of nearly 300 words, I currently have all of them in 4-bar strength. This is wrong. The word 'tard', for example, I don't recall ever encountering after I've first learned it. Yet it says "last seen 2 minutes ago". And I never get it in practice sessions.
It is. Words that you never get wrong will keep fulls strength for two months, then they will drop to one bar. Words that you have gotten wrong will start decaying faster when you get at bit further, but the word strength decay algorithm is far from perfect.
I haven't had problems with the sorting, although it is a bit slow.