I got my Moto-X a few weeks ago, and have been using it without issue on AT&T. Unfortunately, I'm just wrapping up my first trip through Europe with this phone (left my iPhone 5 at home), and I've noticed a very odd thing over the last week.
For some reason, my phone will not re-establish a cellular data connection once it has connected to WiFi (and subsequently disconnected from WiFi). I have noticed this - consistently - in both Germany and Italy. In all cases, once WiFi is no longer connected, I can see that the cellular data network is available (the 4G or E logo shows up, grayed out, next to the cell bars) but it will not reestablish. The only way to obtain a cellular data connection is to restart the phone.
I've tried going into airplane mode; I've tried cycling cellular data. Nothing I can think to try causes the cellular network icon ("4G" or "E") to cycle from gray to white...I simply cannot get back online without a full restart. But once I've restarted it works fine - so long as I don't jump on WiFi.
The phone isn't unlocked; it's an AT&T device, with no APN tweaks.
Anyone have any idea what could cause this behavior? Unfortunately, it's going to be another four or five weeks before I'm back here to test any ideas...but I figured I'd reach out while the issue is fresh.