If related cards are due on the same day, Anki tends to show them one after the other during review or after 2-3 other cards.
By related cards, I don’t mean the sibling cards (which are buried anyway). I am talking about the cards that are related to the same topic, were created on the same day and were first reviewed on the same (or consecutive) days.
This happens despite the fact that I have set the Review Sort Order setting in the Deck Options to “Due date, then random”. (And it is not the case that these cards are some of the very few cards due on a particular day.)
If I create a filtered deck with the due cards and then choose “Random” in the “cards selected by” option, the problem disappears, and these cards are no longer shown close to each other.
So, it makes me think that the random option in the Review Sort Order setting is not truly random, while that in the “cards selected by” option in filtered decks is.
I am doing my reviews on AnkiDroid v2.16alpha97 with the new backend and v3 scheduler enabled. So, it should behave similarly to Anki 2.1.61. However, I not tested this with Desktop Anki because I do most of my reviews when I am not at my computer.
Also, I want to request for an option in the Review Sort Order setting to sort reviews randomly without considering the due date at all. The reason is that if Anki also considers the due date, it first shows all the cards that were buried the previous day (because their sibling was reviewed that day), making it easier to guess the answer.