Iphone 6 Repeatedly asking for activation

[SC_Tiger]

I have an Iphone 6.  Lately it is asking for activation at least once a day.  This typically happens at my desk, where there is little to no cellular reception (quite often it shows "No Service" at the top of the screen).  When I press the button to wake the phone up, it has the white apple on the screen and asks for my iCloud password.  Sometimes it won't let me get through the "activation" until after I get to a good cell area, but then I can get around the activation and it acts like normal.

Anyone got an idea what would cause this?  It didn't do it yesterday - I assume because I was in better cell reception areas most of the day.  I've started keeping it in Airplane mode at work to try to get around this.