Version

3.6.0-beta.12

Reproduction link

play.vuejs.org/

Steps to reproduce

1. press 'toggle expansion of first item' button under 'vapor mode'
2. see item won't be animated
3. press 'toggle expansion of first item' button under 'non vapor mode'
4. see item will be animated

What is expected?

animation should be triggered

What is actually happening?

animation won't be triggered

I expected the transition to trigger when the key of an item in the v-for loop changed, but it didn't.
However, it worked as expected when I disabled Vapor Mode.
It also worked fine if the item inside the loop was a plain element instead of a component.