I am just getting items to plat. I saw today an item count of 1 in Diamond. So it shouldn’t be possible. No idea what it is because I have thousands of cards and there is no way to search by SRS grade.
I do remember opening two review sessions on accident so maybe a double promotion issue? no clue tbh
This sounds like the culprit after looking through things on my end 
If you started doing reviews in one session and then went to the other session to continue reviews, you may have had stale items/already answered items in the queue.
We will put additional guards against “double promotion” scenarios like this one to prevent this 
I will update this thread when the guards are in place.
The item in question would be 广 - Shack - Chinese component mnemonic | HanziHero
We now have some rudimentary but solid guards to protect against multiple sessions / accidental SRS stage bumps
As soon as we detect something amiss (like an item that was already reviewed), we’ll throw up the Stale Session modal asking you to refresh:
Further improvements we’re thinking of doing is verifying you only have one session open instead of waiting for the Stale Session modal to pop up 