Translation of this issue:

Element UI version

2.13.0

OS/Browsers version

MacOs 10.13.6 / Chrome 79

Vue version

2.6.11

Reproduction Link

https://codepen.io/wgcg/pen/bGNLvPg

Steps to reproduce

1. click the switch button
2. Click "create now"

What is Expected?

Check the rules of "activity form" and give corresponding error prompt

What is actually happening?

There is no input in the active input box, but the verification is passed

• • reasons * *
    Reusing the previous formitem instance will not trigger the mounted event of formitem, nor push it into form.fields

Interim solutions

1. Add the prop attribute to the formitem component of "activity note", so that when it is mounted, the component instance will be pushed into form.fields. After switching, the component will be reused, and its prop attribute will be updated, so that it can be verified normally
2. Add key attribute to formitem of "activity form" to avoid reuse

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