[Xiaomi Mi Mix 2S Questions & Answers] PWn3R:
I had a screen break due to it falling on a very sharp corner of an object from about 6 inches up. I took it to a phone repair place locally. They dropped the logic board, camera, front facing camera/charging interface board as well from like 4 feet up onto concrete. The person who tried to repair the screen (which I provided the replacement for) did not follow the instructions on the video either and removed the plastic lining bezel from the phone body (you are supposed to remove the screen from the bezel with a heat gun). They had to send the phone out for micro-soldering to re-place and reattach the antenna connectors for the cellular and wifi antennas. They had to pay for that. I know what the phone looks like inside from watching the videos of how to replace the screen. When they gave the phone back, there was a substantial gap between the edge of the screen and the bezel in a couple spots (atleast 3 or 4 sheets of paper thickness). I ordered a new frame, bezel and screen all in one and replaced it myself (moved all the components from the original phone body to the new one). Everything appears to work, signal levels are good, but the cellular part will not stay connected, and the modem acts like it's resetting all the time. Sometimes it will stay connected to the repeater in the office I work in for 8 hours straight with no issues, and I can text and call. When I leave that area or go home, it doesn't seem to want to roam to service, and instead of switching cell sites it seems to just reset the modem. There is absolutely a possibility that some small transistor, resistor, cap or something else on this board got damaged when it fell. Given that you guys aren't reporting issues with your devices staying on the network, I'm starting to think I need to go back and make some serious noise at this repair place. I am no stranger to working on sensitive electronics, and I was extremely careful not to damage anything inside when I moved the components (and it was already exhibiting this behavior when I got it back from them before I took repairs into my own hands).

That said, I've spent the last two days trying to figure out if I can do anything that might be helpful with QPST and QXDM as well as playing with various additional build.prop configuration. Nothing there that seemed to help. Rolling back to MIUI9/Oreo seemed to help some but was not a magic bullet. I still had to manually configure APNs and find myself needing to reboot or airplane mode every time the device should roam to a new cell site. I am planning on trying to copy the "carrierconfig.apk" file that is part of the system settings off of a Pixel 3 XL onto the Android Pie MIUI10 beta to see if possibly Xiaomi has something jacked there, but since you guys aren't reporting issues, I am seriously starting to suspect that something is physically damaged after that drop on the logic board, but the intermittent behavior and the fact that the signal looks correct and normal when it's working is going to make it nearly impossible to identify the cause.

As a side note, there's a Mi Mix 3 on it's way from GearBest....

---------- Post added at 04:00 PM ---------- Previous post was at 03:10 PM ----------

So on mine, I can't get it to connect whether VOLTE check is enabled or not. At the office I'm like 10 feet from a repeater, and it seems to connect on LTE/VOLTE (if that's toggled on) very quickly. I have VOLTE enabled on my Verizon account. On the extender, I can make calls on VOLTE, but can't call without VOLTE enabled. I can't get it to connect to VOLTE with the VOLTE carrier check enabled, I have to shut that off and manually toggle. I am noticing massive inconsistencies in the configuration information contained inside the carrierconfig.apk that is loaded in the system build by Xiaomi. I don't see a smoking gun there, but there's a metric crapton of differences.

If I am not next to this Verizon repeater, it usually takes multiple airplane mode cycles or reboots to get onto LTE, it just sits on 1xRTT forever, no texts or data come through when stuck in that mode. Any type of cellular roaming that should happen seems to just cause a radio reset, and it goes to blank bars with X and then it acts like it can't find a network to connect to for a while or goes 1xRTT with full bars and keeps resetting every 20-30 seconds.