Currently, the scope passed into GetValidationErrors(ElementScope) gets synchronized in IsValid(ElementScope), which then throws a MissingHtmlException with Coypu's default message. The message should be "Could not find validation error field. This could be due to wrong markup.".
The attribute access ("aria-describedby") returns null if the attribute could not be found, which would lead to a NullReferenceException later on.
The validationErrorsScope in the next try block is not synchronized in it, which means that the exception gets thrown when accessing the scope's InnerHtml property.