Thanks, please keep working on this one. It may not be a fundamental problem, but it is still a real problem when it happens.
Like hz, I use the Android App, but I haven’t been seeing much repetition recently. I’ve slacked off on adding new words, and my queue has fewer than 200 words. During review, occasionally the app pauses and spins for a few seconds, and then it repeats the exact same card. Since it only happens 0 to 2 times per review session, it doesn’t bother me, but maybe these are clues as to what is going on.