In russian course, whenever i practise late at night, number of cards to the next milestone freeze at some random number, i.e. first several cards are counted as I answer correctly, until the number freezes. Sentences themselves are not affected. Interestingly enough, this does not happen during daytime.
This is not fixed. I've been continually having this problem with Spanish.
I practiced up to 150 cards this afternoon then stopped. Now, at 1AM (UTC-8) the count refuses to go up. It will go up and down between 152 and 153, and back to 150 if I log out.
Are you talking to different servers; maybe you have a synchronization problem between them?
Or your system is a bit confused about what day it is and counts totals in an error-prone not entirely logical way?