here is my [codesandbox](https://codesandbox.io/s/react-hook-form-unregister-v6-forked-19446?file=/src/index.js), I'm manually registering two fields, if I click submit w/o entering any data I see required field validation, which works fine and if I unregister "lastname" it removes error from last name, however,

The problem: first name still shows required validation even if I enter data.
I tried removing manual registering a field and it work fine. But that is not my requirement.
Any help. Thank you.