I have the same problem as well and after waiting to chat with Verizon Support for 3+ hours, the solution provided was the phone number to the "Do Not Call Registry" ???? I'm not sure how that's was suppose to answer my question. Did you ever find out what this was about?
Verizon uses a 866 number to provide simultaneous ring to Nomorobo. I don't know if everybody uses the same 866 number or if each person uses a unique number. When I get a Robo call my phone rings once and Nomorobo blocks the robo call. The 866 phone number assigned to me does not show up as being dialed in my Verizon Fios Digital Voice call logs. If you block the 866 phone number used by Nomorobo then Nomorobo will no longer block calls.