It is a representation error I think. The counter stops when you get to max number of kills/turns/spells cast or so.
In AI you need to win in 10 turns or less but when you win in 11 or more turns, the objective counter still says 10/10 but is red instead.
If you hit the exact max number it will say 10/10 but will be white and bonus granted.
If you cast 2 creatures in 2 or less it’s the same but cast 3 and it will show 2/2 but in red text instead.
Same with create 4 or more tokens and cast 3 or more supports costing 10 or less in The Brothers’ War. I had a stack of twenty token vampires at the end, and it was listed as 4/4. I also cast more than 3 supports and only 3 were listed. I was looking forward to getting truly ridiculous numbers of token creatures too…
Hi Everyone. I spoke with the team, and it appears this was an intentional UI change. Having said that though, based on player feedback, the team has decided to revert it in the upcoming 2.8 build.