De-ranked after a win!

Just went from diamond 2 to diamond 3 after a win?!
I’ve got a screenshot but don’t know how to post here.
Playing on iPad.
Any idea what has caused this or if it’s a bug? Could it be due to a previous disconnect (iPad often crashes)?

https://us.forums.blizzard.com/en/hearthstone/t/how-to-share-links-to-screenshots-videos-and-replays/2242

Upload the image onto an image sharing site and then follow the instructions abow.