Software hangs after clicking "I Know this word" a few times

My browser hangs after clicking “I Know this word” a few times. The first 10 or so times the response is speedy, after this it is delayed / slow, and sometimes it freezes completely. I am on the first Russian lesson.

My browser is Chrome.

@tomac120 - Thanks for reporting this. We have had some other reports on another thread (Slowness Issue When Saving Lingqs - Language Forum @ LingQ) and are looking into this now to see what may be causing this.