Yesterday, while at work my phone worked until half a day and later in the afternoon I noticed no signal. Being inside the building I thought the signal must have been week so I didnt pay much attention. Later when I left work and the signal did not come back on even after restarting(at restarting I saw something funny. There was an unlocked padlock sign with custom written on top of it underneath "Samsung Galaxy Note 3" logo), I went to AT&T store and they tried to replace the SIM and suggested hard reset. I tried that but signal did not work. Replacing SIM didn't work either.
Then, I ended up flashing the firmware using Odin to lollipop (5.0) and the signal came back. I made a call or two to check but then I noticed the mobile data didnt work. I called tech support and she said she was going to reset the APN details and I had to restart the phone. I restarted the phone and the signal was gone and the phone went back to "device status=custom". This custom screen shows up when rebooting as well with an unlocked padlock underneath. This NEVER happened before for the 2 years I've had this phone for.
No one tried rooting this phone. The phone has been in my possession all along and was purchased brand new from ATT 2 years ago. Infact, Its just coming off contract in a few weeks.
I've tried flashing the firmware zillion times and it does the same thing. The signal comes, I test it, it works, device status =official when it works, then i restart and it goes back to custom and the signal disappears.
Anyone with any suggestions on what the heck is going on here?