Hey guys, I'm not sure if this'll help, but I'm still on 4.3 and I've had similar network issues to the ones described in kitkat. I have no way of knowing whether my issues are worse or better than they are on kitkat, since I haven't tried it yet. The reason I was reading this thread in the first place is that I'm planning on upgrading to kitkat in the near future. This is the first Android phone that I've bought for myself, and I did a large amount of research into ROMs, rooting, network compatibility, and just the Android OS overall before I decided to go with the T-mobile model. I've had the phone for about a month, and I haven't had time to do research on whether or not the Kitkat update could prevent future flexibility, so I haven't allowed any OS updates and I'm still running stock Android 4.3 and the MI7 baseband.
Overall, I've had few issues and I'm really enjoying Android even in its stock form. The reason that I'm commenting is that I have on probably 3 or 4 occasions had a problem where my network data stops working. The status bar icons still indicate a signal, but the phone won't load any Web pages. I've found that the fix is to quickly switch airplane mode on, then off again, and then it's back to working great. It's probably been about a week since it's happened to me, but it sticks out since it's one of the only problems I've had. Anyway, I thought this information might be useful to you guys, since it sounds like I'm having the same problem, so that might mean that it actually doesn't have to do with the Kitkat update. Then again, it's also entirely possible that the Kitkat update made any problems worse. I like to get as much data as possinle when im in such situations, and being that you guys are helping me out anyway, I figured id pay it forward.
Some other things to note:
Mobile plan: T-mobile prepaid 5Gb data / unlimited messages / 100 minutes for $30
APN: fast.t-mobile.com
APN Protocol: IPv6
APN Roaming Protocol: IPv4 (I set data roaming to on when I first got the phone, but as far as I know my prepaid plan doesn't have any roaming allowance.)
I never touched the APN, so I'm not sure if the phone came with that APN or if it was installed automatically after I activated the SIM. One thing that I did notice just yesterday when I was browsing through the settings app, is that the setting "Auto network switch" ("Auto switch between Wifi networks and mobile networks") was unchecked. I actually didn't even realize that this particular list of settings existed, since you have to press the hardware menu button while looking at the list of wifi networks to get to it. I only saw it when I was reading through the manual. The manual I have is actually dated sometime in February, so I think it's based on Kitkat and not Jelly Bean which is what I'm running. The "Auto network switch" setting is not listed in the manual, so it may not even exist in Kitkat. The path to get to it is Settings > Connections > Wifi > press hardware menu button > Advanced > "Auto network switch."
It seems odd, since I've mainly used my phone on wifi, but when I have used mobile data outside of the house, I haven't had any problem transitioning to cellular data. When I did have a problem, it occurred in the middle of a Web browsing session, and like I was saying, cycling airplane mode restored the connection no problem each time. I only realized that this setting existed and enabled it yesterday, so it's too early to say if it made a difference, but it seems like a no-brainer that that option should have been set to on by default. Like I said earlier, I only had the problem on 3 or 4 occasions, so when it did happen, it wasn't happening all of the time.
Another thing that I should note is that I'm in Orange County California, and as far as I know, almost all of my coverage is LTE. On off peak hours I've gotten speeds of 30+ Mbps down AND up, and during peak hours around 12 down, 8 up. Although, now that I think of it, one of the times when I had an issue, I was in a parking lot and getting slower speeds which could have been HSPA+, so it could be like one of the commenter's was saying, that the problem occurs when switching from LTE to HSPA+ or vice versa. It could be that the reason that I've had so few issues is that I've been in almost exclusively LTE areas.
This might be a total noob suggestion, but if you're grapsing for straws, that setting I mentioned is something to check out.
