"isValid" does not work in "production" mode correctly for "useFieldArray"

Describe the bug

isValid from formState behaves itself differently for dev mode and production build by using useFieldArray

• dev mode is launched by react-scripts start
• production mode is built by react-scripts build and served by any server. In my example it's express server

To Reproduce Steps to reproduce the behavior:

• Please clone the git repo with reproducible scenarios:
• Make npm install
• Run npm run dev:make-build-and-serve:run

First test-case

1. Go to localhost:8001 and check that isValid: false is shown on the bottom of page.
2. Enter any Quantity and Product ID for Heading section. isValid label will be changed to true
3. Delete Quantity or Product ID. isValid label will be changed to false
4. Validation will be shown under the fieldname
5. Select Heading2. First Heading will be closed and inputs should be unmounted from DOM.
6. Enter any Quantity and Product ID for Heading2 section. isValid label is still equal false.

If you perform the same scenario but for dev mode (npm start), on the 6 step isValid will be changed to true

Second test-case

1. Go to localhost:8001 and check that isValid: false is shown on the bottom of page.
2. Enter Quantity OR Product ID for Heading section. Second field must be empty.
3. Select Heading2. First Heading will be closed and inputs should be unmounted from DOM.
4. Enter any Quantity and Product ID for Heading2 section. isValid label is still equal false.

If you perform the same scenario but for dev mode (npm start), on the 4 step isValid will be changed to true

Codesandbox link (Required) Codesandbox: Please make sure that you go to the Deployment section and made a production build and deployed it to Netlify

Then please click Visit Site link

Expected behavior

• isValid must behave itself equally for production and dev builds.
• For production build isValid must behave itself equally how it works for dev build.

Screenshots

Desktop (please complete the following information):

• Windows 10 / Ubuntu / OS:
• Browser Chrome / Firefox / Safari
• Version 88.0.4324.150 / 85.0 / 13.1 (15609.1.20.111.8)

Smartphone (please complete the following information):

• was not tested

Additional context This issue is reproducible only by using useFieldArray

isDirty and other flags are also affected