SOLVED!     Because the other device that I have in my network had always connected properly to its phone app whether or not WiFi was turned-on as long as cellular was on and vice-versa, I refused to consider outside-my-normal pattern of thinking that things ought to work if I simply add port-forwarding to the raspberry pi in an analogous manner.  But adding the pi seemed to "break" that internal routing from apps-inside-network to devices (including pi) in network.   I finally broke down and captured packets and analyzed with wireshark.   I'm pretty rusty with that tool, but what I discovered looked like a double-nat issue (My MX is in a DMZ on a google fiber box).   Hence, I added port forwarding  (in addition to the DMZ), and now all is well!   I do admit that I am still baffled why it worked for the other device  in my network - it has for years!    But I am happy that all is working, and I apologize for not having done more diligence (wireshark) before posting  in the first place.    An ever-exuberant Meraki fan! -Mike ... View more