Mobile data unavailable

Question

Hello world,
my name is Luca, from Rome, Italy.
I bought a Xperia Z3 Compact in September, I found it to be an awesome device, but since the first day I got a strange behaviour on mobile networking.
Often even if the device shows a very strong signal like HSDPA+ at full strength ( 4/4 bars ) still my mobile internet connection doesn't work at all, and the only way to reenable its functionality is to turn on "airplane mode" and off again..
Because of the issue I contacted the Sony assistance service that guided me to the closest repair center, and in less than 2 weeks they gave me the device back, unfortunately with the very same issue still there, attached is the repair recepit that claims that the issue was not found at all, the translation of the note field is:
"Issue not found, software updated, touch parameters calibration ok, recharge and power consumption verified.
Data connection - Wi-Fi ok, if the issue will show again, proceed to configure internet/MSS setting.
Back cover broken, fixable out of warranty." https://www.dropbox.com/s/7ttaixyqp1xqx59/recepit.jpg?dl=0
There was also a minor issue about strange "noisy" behaviour / hyper sensitivity of the touch screen that was actually fixed by the software update ( the Lollipop update was rolling out those 2 weeks here in Italy ).
The network issue itself is not 100% reproducible because some lucky times the issue doesn't show, but I managed to get a couple of screen recordings showing the issue, in both recordings I'm trying to access some internet service ( googling things or accessing some youtube clip ) but the browser and the YouTube client simply get stuck on loading. Note also that no "Network not available" alert is shown and that the signal icon in the top bar shows a full power HSDPA+ connection available. https://www.dropbox.com/s/149fflg1ayxwcyk/record.1.mp4?dl=0https://www.dropbox.com/s/yjpzwgkzbj4y29y/record.2.mp4?dl=0
For sake of completeness my carrier is TIM, with a LTE enabled plan.
The device is now configured to use 3G/2G networks only but the issue arise in 4G mode too.
Also the "stamina mode" and the "background data queue" are set but I spent various days trying the different permutations of these and other settings looking for a combination that would solve this thing, with no success.
I also already tried disabling bluetooth, again with no result.
The device has "developer options" enabled but is not rooted nor the boot loader unlocked.
I understand the people at the repair center cannot deeply investigate every single device they receive but I hope you will understand my disappointment in having a 500€ device that simply has its most powerful feature broken.
If you cold put me in the right direction to solve this issue it would be great.
Thank you very much for your attention and in advance for your help.
Luca Castoro

Answer 1

@uliwooly This is the screen recording I captured yesterday evening, forgive me, because the software repair moved the icons in the notification bar to their original location I was missing the "airplane mode" icon even if it was in the very center of the screen ( I was looking for it where I placed it in my previous configuration in the lower right corner ) so the video is slighlty longer than necessary.Also i forgot to change the capturing mode from landscape to portrait so there are black bands on the screen sides. https://www.dropbox.com/s/ye9a687jrncoja5/record.3.mp4?dl=0 Tomorrow I'll ask a friend to swap for a couple of days our devices so I should be able to investigate if it's a SIM related question or a device fault.I really don't think it will show itself as a SIM related problem as I can always make/reveive voice calls or SMS, but at least I'll remove any doubt about this thing.