forms – React blocking UI when waiting for XHR

Lately I’ve been using React + Formik to create great user experiences.
I’ve a question about blocking the UI when the XHR is still processing.

Imagine a register form, with only a sign up button. As soon as the button is clicked, I disable the button, show a loader and set it’s cursor to default. All good so far.

In that same view of the webpage there is also a link to “Already have an account? Sign In!” (and a view other hrefs). The “Sign In!” part is an URL, which is still clickable. What do I do in this situation? Should I block the “Sign In” href?

Because when the user clicks “Sign In!” when no response has been received yet from the backend. It either returns 200 registering was succesful and redirects. Or it returns a validation error in which case the component is unmounted and React gives errors.