Cannot load session. ASL flashcards

I created new flashcards for vocabulary consisting of English prompt with custom image column (filled with animated .gifs). I got to 27 vocabulary terms and attempted to test-run the course ( https://www.memrise.com/course/2054191/asl1-alt-vocab/ ).

But I am getting an error at bootstrapping “Cannot load session”

Is this supposed to be the case? I really limited the framerate for the images. I guess they average 2-3MB per animation.