[Android Q&A, Help & Troubleshooting] PeterDLai:
This is what I experience every once in a while on my HTC Droid Incredible 4G LTE (stock but rooted):

1. I'm connected just fine to the Verizon 4G network with fast speeds through wi-fi tethering. The phone is sitting in one spot the entire time.

2. All of a sudden (at random intervals), data stops flowing and I can't access any websites on either my tethered computer or on the phone itself.

3. I check the status bar on the phone and it still displays a 4G icon, the arrows are not blinking to show any activity, but the icon is there.

4. Sometimes it's able to reestablish connection by itself anywhere from 5-10 seconds later. Other times the loss of connectivity endures for an indefinite amount of time.

One thing that fixes it 100% of the time is toggling mobile data off and on.

I was able to do a logcat of the radio buffer on my phone and tried analyzing it myself to see if I could figure out what was going on, and what I notice is that around the time that I lose connectivity (roughly around the time 01:05:40), I start to see these lines get repeated over and over again:

D/CDMA ( 708): [HtcRadio] 3GIND:1
D/PHONE ( 708): phonebase getDataActivityState

And the line that is missing during the time that I have no connectivity (as opposed to when it's working) is this:

D/CDMA ( 708): [CdmaServiceStateTracker] RUIM imsi=*******59888340

Around 01:15:52 in the logcat is when I toggle mobile data off and on (and as expected, data starts working perfectly again).

Do I need to do a different logcat or is there enough evidence in this to show what's wrong with my phone?

FWIW, I also have a Samsung Galaxy S III and tether to it in the same exact fashion (same SIM card, network) but I have not been able to reproduce this issue on that phone. I prefer the HTC for its stronger reception in my house, getting around double the speeds of the GS3, but it seems to be at the cost of stability (perhaps the HTC has a hardware defect?)

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I then tried an unofficial CM10.1 ROM to see if the RIL is the culprit.

I was able to reproduce the issue on a CM10.1 build and got a radio logcat available here. Just like the stock ROM logcat, it looks like something is happening around the time I lose connectivity (sometime around 18:58) which causes it to start producing these lines repeatedly:

06-18 18:59:01.202 D/RILJ ( 942): [UNSL]< <unknown reponse> {1}
06-18 18:59:01.212 D/RILJ ( 942): responseDataCallList ver=6 num=20
06-18 18:59:01.212 E/RILJ ( 942): Exception processing unsol response: 1010Exception:java.lang.RuntimeException: getDataCallState, no ifname

I have no Android development experience so I wouldn't know how to debug this, unfortunately.

This time when the issue occurred, the phone automatically regained connectivity (without needing to toggle mobile data) a few minutes later (roughly 19:02) and the only evidence I can see of something happening around that time is the appearance of these lines (which normally appear occasionally throughout the duration that connectivity is still active):

06-18 19:02:05.299 D/RILJ ( 942): [0224]< DATA_REGISTRATION_STATE {1, 3602, null, 14, null, 20}
06-18 19:02:05.309 D/CDMA ( 942): [CdmaLteSST] handleMessage EVENT_POLL_STATE_GPRS
06-18 19:02:05.309 D/CDMA ( 942): [CdmaLteSST] handlePollStateResultMessage: EVENT_POLL_STATE_GPRS states.length=6 states=[Ljava.lang.String;@4114f8b8
06-18 19:02:05.599 D/RILJ ( 942): [0222]< OPERATOR {Verizon Wireless, , 31000}
06-18 19:02:05.599 D/CDMA ( 942): [CdmaLteSST] Set CDMA Roaming Indicator to: 1. mCdmaRoaming = false, isPrlLoaded = true. namMatch = true , mIsInPrl = true, mRoamingIndicator = 0, mDefaultRoamingIndicator= 0
06-18 19:02:05.599 D/CDMA ( 942): [CdmaLteSST] pollStateDone LTE/eHRPD STATE_IN_SERVICE mNewRilRadioTechnology = 14
06-18 19:02:05.599 D/CDMA ( 942): [CdmaLteSST] pollStateDone: oldSS=[0 home Verizon Wireless 31000 LTE CSS not supported 54 4 RoamInd=1 DefRoamInd=0 EmergOnly=false] newSS=[0 home Verizon Wireless 31000 LTE CSS not supported 54 4 RoamInd=1 DefRoamInd=0 EmergOnly=false]
06-18 19:02:05.599 D/CDMA ( 942): [CdmaLteSST] pollStateDone: hasRegistered=false hasDeegistered=false hasCdmaDataConnectionAttached=false hasCdmaDataConnectionDetached=false hasCdmaDataConnectionChanged=false hasRadioTechnologyChanged = false hasChanged=false hasRoamingOn=false hasRoamingOff=false hasLocationChanged=false has4gHandoff = false hasMultiApnSupport=false hasLostMultiApnSupport=false

Any experienced Android developers know what's going on here?