NSTaggedPointerString stringByReplacingCharactersInRange:withString:]: nil argument in iOS13
This looks like a bug on iOS when the user taps more than once on an auto-completion field that appears after a new email message with the code of 2-factor authentication was detected. Please check this out: http://openradar.appspot.com/7428013
As a quick fix, you could do the following, of course, if you have the access to the web page content where you have an input field for the one-time validation code. Disable the autocompletion for that input control, so it looks like this:
<input id="one-time-password-textfield" autocomplete="off"/>
Then you (and me) will need to keep track of that OpenRadar ticket hoping it will get fixed anytime soon ;-) Once fixed, the auto-completion can be re-enabled back in the HTML code.