Hover hints missing
Is there a new A/B test where many words don't have hints when one hovers? Once this happened twice in one lesson, I tried all of them, and many words had a kind of white on white starburst design when I hovered.
I think you're describing the standard design that pops up when hints happen to be missing. Obviously it's more commonly seen in beta-stage trees.
One never knows what they might be testing, but I'd suppose you got some sentences that just haven't been set up correctly in the system.