After a field becomes invalid and then the user starts typing, the error message will go away as soon as the input is valid. But if while typing, if it becomes invalid again, the error won't come back until the field is unfocused. This is not really best practice for user experience. Must either remove this feature or maybe show the error back when field is invalid again while typing instead of having to wait till blur.

See the following studies for more info:
https://baymard.com/blog/inline-form-validation
https://alistapart.com/article/inline-validation-in-web-forms

Sometimes when unchecking the checkbox or when selecting less than 3 of the multiple select options and then clicking the submit button directly after will not work. One needs to click somewhere first for the error message to show and then the submit button can be clicked.

When clicking submit, the first invalid field should be focused. It doesn't work on radios and checkboxes.