UITextField: backspace doesn't delete the first character

Question

I have a UITextField with a formatted string.

I can't figure out why a backspace press works fine for every character deletion except the first character?

My code:

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    
    let formatter = NumberFormatter()
    formatter.usesGroupingSeparator = true
    formatter.numberStyle = .decimal
    formatter.decimalSeparator = "."
    formatter.groupingSeparator = " "
    
    let textString = textField.text ?? ""
    guard let range = Range(range, in: textString) else { return false }
    let updatedString = textString.replacingCharacters(in: range, with: string)
    let completeString = updatedString.replacingOccurrences(of: formatter.groupingSeparator, with: "")
    
    guard let value = Double(completeString) else { return false }
    numberFromTextField = value
    
    let formattedNumber = formatter.string(from: NSNumber(value: value)) ?? ""
    textField.text = formattedNumber
    
    return string == formatter.decimalSeparator
}

A gif with the problem behaviour: CLICK

Where is my error hides?