This problem has been plaguing all three 8x phones in my house. It happens every day. I spent a lot of time trying to find a root cause, and I finally found something that seems to be at least related, if not the cause.
Every time this happens, I can go into Settings -> Email+Accounts, and my Microsoft account is in the process of syncing. It goes on for a very long time, and while it's happening, texts do not work, chat goes offline, and my other email accounts will not sync. For example, I can open up Yahoo or Gmail, and type an email. But when I hit send, it errors that it is unable to send at this time. If I type a text and hit send, nothing happens. The exact same behavior happens on the other two phones.
I have changed my account sync for the Microsoft account to once per day, and now the problem happens only once per day when that account syncs. Exactly the same after making the same changes on the other two phones. The only way I have found to reliably fix it is to toggle data on and off (airplane mode), and then reboot the phone. This process has fixed all three phones each time they do this.
Not sure what is going on with the Microsoft account sync, but it seems to be tied to the issues we are having.