I recently started Russian 10,000 words by frequency part 2. Sometimes it is rejecting correctly spelled words. Once it rejected four or five, though when I tried again the next day it was OK. Just now it rejected izdevat’sya and I decided to put this word on Ignore. I am not sure if it is a Memrise technical problem or a problem with my own Internet connection, although I never had this kind of problem with part 1 of the same course.
It appears that words are being rejected if, as in the example I gave, I leave out the (nad +inst). So it may be a stricter programme rather than a technical fault.