I don't know if this is a known problem for your staff, but this tab doesn't do what it's name says it does. For example, I played Urgot yesterday and he is so down the list even though I played him after the Sivir game. I thought it could be related to ranked, but the Sivir game was a normal draft - just like the Urgot game.
This could be the main reason why championmasterylookup.dermetheus doesn't show that particular information precisely as well.
It may not be an important feature, but I like to see which champs I didn't play in a while and maybe go back to them, since so many times I don't know what to play and try to use this feature, and it hasn't been working properly for a while now so I thought it could be caused by me in a way.