Version

15.7.1

Reproduction link

https://codesandbox.io/embed/vue-template-6g1bj

Steps to reproduce

Click the button.

What is expected?

Do not delete slot content

What is actually happening?

Solt content has been deleted

I don't have this problem when I only use vue static resources
https://codepen.io/linkontoask/pen/rNBpGKd
And I have such problems in apps that I built with vue-cli.