I was just about to post a bug and found this thread. As I learned in another thread it is not an issue for all of us. For some texting still seems to be available. So that means they have not taken it away to prepare for the update or something but it is really a bug.
For me it is now completely persistent in every save, new or old and completely irrelevant if the Zois are best friends or just met. The option to send them a text message is permanently greyed out, only responding is possible if they text you.