Unfortunately I've done the reviews now, so I can't show you the stats page.
As far as I'm aware, nothing changed between today and yesterday. I synced to my computer, which did do a reschedule, but that's never caused this sort of issue before. Even if the reschedule did cause this issue, im still confused as to why I didn't see those extra cards when reviewing.
The issue at hand is that the stats page suggested I had 500 new cards due today in the future due graph. This is surprising because, as mentioned, no change to my study habits was made, so i wouldn't expect any sudden increases in the amount of due cards. It's also surprising because I had 880 cards remaining in my backlog yesterday (after removing the buried cards) and today I only have 1100 (again, after removing the buried cards), which suggests that in fact only 220 or so cards were added to my backlog, which contradicts the stats page.
I'm not exactly a 2-button grader. I use again and good the most, but do use hard and easy about 2% of the time each.
I'm not certain which deck has the unexpected workload. I think it's the deck shown, because the stats page suggested 200/500, or 40% of my due cards came from that deck, when that deck only occupies 15% of young and mature cards by volume, but of course I can't be sure because of difficulty and different weights etc. The only average workload I have a finger on is the workload for my main deck (which contains all the other decks for easy review), so I can't look at the due cards and easily tell where the unexpected workload came from.