AT&T LG V10 messaging app changing the area code, how can I stop this?

[AC Question]

ATT LG V10 messaging app changing the area code

I have an ATT LGV10. When I send a text message to one person using the standard messaging app, it changes the area code after I send the text. Specifically, it changes the area code from 414 to 424. Then I cannot respond to any messages for that person. I have tons of other contacts and messages in the 414 area code without this issue.