At first I thought I was hallucinating, but I did it again and again and it’s just as I saw the first time:
my opponent’s rank suddenly changes after the page is loaded!
Here is the game:
My opponent now is 11k.
I click on the next game (circled number on top right) then I click the “back” button on my browser and while the page is loading the rank is 12k, then suddenly becomes 11k.
If I just refresh the page, the rank is always 11k.
It could be that the rank you see first is you opponents rank as it was as the game started. When the games page is fully loaded it updates the user data with an additional request to the server. If your connection is slow, you can observe it visually.
Just started noticing this, as well. Seems like there’s an initial request for the rank, and then another request when the page updates that gets a different rank. The second one seems to be correct.