During the past couple of months I’ve noticed that the more I progress on a review session, the less responsive the website gets. This happens on Safari on iOS 9 both on iPad and iPhone (this also affects the AlliCrab iOS app).
The performance decreases gradually, but I’d say it starts to represent an issue if the review batch goes over 30 items. Haven’t tested on iOS 10 as I haven’t upgraded, but I thought it was worth mentioning.