Please try it again and let me know while it works now. I fixed something that might have been an issue, but I'm not sure if it was related to your problem or not.
In general, you're not supposed to have problems connecting, with the exception of when your phone is connected to some corporate networks that do very specific things to block WebRTC, i.e. Accessing via a normal cellular provider should not require anything special. Which cellular provider one are you using?
AT&T gigabit fiber should also not be a problem -- although if you have the somewhat buggy Pace modem that may make it a bit harder to make connections than if you have the Arris BGW-210. It assume you let it try more than once to make the connection? Also, I think your Netgear nighthawk is not anywhere in between Camect and your phone in the away-from-home scenario you're describing, so it shouldn't matter either.
Could you try it again, letting it attempt to connect at least 3 times, and then use "Report Bug" from the top level page to submit a bug report so that we can see what information is being reported? (You should be able to Report Bug from the top level page even though the connection doesn't succeed. Make sure to check the checkbox to include browser logs. If you have any problems with Report Bug, send us email with the time (and timezone) at which you tried to connect, and the email address you used to activate your Camect and we'll see what we can figure out.)
(By the way, you can also do this test when you're physically at home by turning off your phone's wifi to see if you're able to connect through the cellular network.)