I have had the issue as well and also where the signal goes from 3G to 1X. Not sure if network or device issue. It does not happen enough to be an issue to dig into, so far. Happens maybe twice a week for a few seconds. One time, I had to reboot to get out of 1X.
I wonder that if it is the device, if is a power settings issue, since keep mine on the battery saver mode. The device sometimes seems slow to reaquire signal when in this setting, after coming out of "sleep" when unlocking.
That said, if your are in NY and I'm in KY, that is a broad network issue, so probably a device issue.