This has happened to me before with the phone's other radios, cellular and wifi. I haven't noticed it with 4g because I don't use 4g that much. I suspect it can probably also happen with bluetooth as well. I've tried turning on wifi and it will say it's connected but there's no wifi bars and the connection speed is -1MBPS and the internet won't work. I've also brought my phone out of airplane mode and had it tell me there was no signal when I'm positive the signal is just fine. I'm pretty sure this is a software bug. It doesn't seem to happen to me that often and there's really no way for me to tell what's triggering it, so I just do a quick reboot and go on with my day. I probably go for 2 weeks straight without a reboot before this problem affects me, just to give you an idea, so it's more of a mild annoyance.
