Root Connectivity problems with Unlocked N5 on AT&T

[egernant]

Here's the series of events:

• Unlocked Nexus 5 on AT&T prepaid plan started randomly disconnecting from cellular data, saying "No SIM card - Emergency calls only". A reboot would fix temporarily.
• Fixed some settings at the AT&T store and tried a brand new SIM card - didn't fix the issue. AT&T said they've done all they can do and that it must be a device issue.
• Google sent me a replacement N5
• Replacement N5 now suffers from a similar, yet different issue. Instead of getting the No SIM card error, I am getting cell service but no data. I see the typical signal icon in the upper right of my screen, but it has an exclamation point next to it. Happens as soon as I get off of Wifi. Reboot fixes it temporarily.

Not sure what to do - that's two phones with similar issues and AT&T can't help. I'd like to request another phone, but that didn't work the first time. Is this a known issue? Would flashing a trusted custom ROM fix the issue by chance? I'm stock unrooted Android currently, but am certainly willing to go down the custom ROM path. Any other fixes that could make sense?

Thanks!

 

[Hook]

I had a similar problem when I first got my Nexus 5 (I use Gophone as well), but I've always gotten great customer service from AT&T. Try calling them. Explain what you and the AT&T store has already been through.

In my case, I was getting connectivity but no LTE. I had gone to the store, they had tried a new SIM and other tings but couldn't find the problem, so I called the customer support number. They double checked the provisioning, tried a couple of things, having me reboot several times. Finally they sent me an app to download to collect data. They also collected data from the towers near my. They sent the data from both my phone and the towers to some kind of network troubleshooting center in Washington state (I'm in VA). 24 hours later I suddenly had LTE and everything has been fine since.

And, no, I wouldn't count on a new ROM solving the problem. I'd solve the problem first.