Same here, in 07/04 the achievement didn't compute after winning the match with the 5 vannila creatures in battlefield, including Yargle and Yargle and Multani.
Then, the next day I've built a 5 color commander with just vanilla creatures, cast 5, won by crewing a spacecraft and still no changes in the achieviment
https://mtgarena-support.wizards.com/hc/en-us/requests/4696315

In this request, Arena support crew have considered the issue solved, but we are 5 days from ending the achievement and I still haven't got it.

Same problem with 0 creature spells

Same. Achievement for vanilla is not unlocking and/or registering. Frustrating.

Have same issue verified I casted 5 vanilla creatures and won didn't get achievement

I just won a long game meeting all of the requirements of “Death by Vanilla” and was not credited with the win. I also played 5 games meeting all of the requirements of “A Frog of Culture” and was not credited with the games played either. Very frustrating. Please credit for both ASAP.

Check the small text on the achievement. You have to cast at least 5 creatures during the game. That being said, this achievement didn't work for me in a game where I did cast 5 vanilla creatures and win.