Same problem here. I came back from a little break hoping to use Lingvist but whatever changes have been made to it seem to have broken a lot of things.
After 50 new words I got a pop-up that I reached the end of the course, moved on, repeatedly got a pop-up that I needed to rest (20 minutes in mind you) then after repeated presses to get new words it vanished.
However, now after every word I get a screen that I've reached my word limit which I need to click away. I hope that's a bug. If so, I don't get why nobody spotted that since many people are running into it. If not, it's a terrible, terrible UX flaw.
We can't even submit a bug because that feature is for paying users only? Really?