I THINK THE ISSUE IS FIXED.
I tried Tivo Support again after my iPad starting freezing when streaming video. Within the first 5 minutes of the call, the agent (William) asked if I had FiOS. And once I confirmed I did, he asked me if I had a MI424WR router, which I confirmed. Then he asked how I connected the Roamio to the router and I told him Coax and Ethernet (same as the previous Premiere unit). He immediately told me that's the problem - since I am using MoCA with the Mini, and the FiOS network in my home is already MoCA enabled, connecting the Roamio with the Ethernet in addition to Coax is causing the Roamio to try and set up a new MoCA network and that will conflict with the Verizon network (or something along those lines). He instructed me to disconnect the Ethernet and use only the Coax connection. It's been about 2 hours since then and everything is working 100% perfect - iPad streaming and Mini.
Thank you William for your help! No thanks to all the others at Tivo who were not able to help me fix such a simple issue!!!
If anyone from Tivo is reading this, I really hope you understand just how poor the support has been on this issue. This could have been resolved on the first call, without me having to go nuts troubleshooting everything in my house. And, why don't your instructions state that you can't set it up the way I had it if you have FiOS - all I did was follow your instructions!
I hope this helps others who have similar problems....