Exact problem as OP, except that it began as soon as I downloaded (AND PAID FOR, Verizon) the app a couple of weeks ago. I have my account set not to take calls that block caller ID, and I would see the number of anonymous or unknown callers. Now I just get "UNKNOWN CALLER" and no number. That's bad. Even for callers not in my contacts, I will frequently know if it's a call I want by the number. Now I don't see it. Verizon, an app applying a database of known spam numbers is a good idea, one I'd pay for. Substituting a number, not in contacts and not on spam list, for "UNKNOWN CALLER" is a terrible idea. In short order it is going to lead me to cancel it, and tell people not to get it.
Unless, of course, you do something.