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[Discussion] LTE/4G connectivity issues, Global Beta 9.5.9 (problem exists since January 2019)

2019-04-11 22:32:31
6328 24

I have a Mi Mix 2S, M1803D5XA, 8/256GB model, bootloader unlocked, running Global Beta ROM 9.3.28 with baseband version AT4.0c2.6-303-0325_2303_ea9c837. The network operator is Telefonica/O2, the service provider is 1&1. LTE coverage mostly B20/800Mhz in a rural area.

After losing 4G/LTE connection, my phone does not reconnect automatically with the available 4G/LTE network (B20, 800 MHz). I have to change the default preferred network settings (LTE/TD-SCDMA/UMTS) to "LTE only" or "LTE/CDMA/UMTS (auto) PRL" and only then the phone reconnects to the available 4G/LTE network immediately. Rebooting/restarting the phone also helps to reconnect. So I think I have to restart the modem to trigger a reconnect. If I just put the phone on the windowsill and wait for it to reconnect the modem sometimes seems to "freeze", the phone indicates a 4G/LTE connection (four out of five reception bars?), however, there is no internet connection. Again, rebooting/restarting the phone helps.

Also, if the phone has to switch from 4G/LTE to 3G or 2G it does not aggressively reconnect with "better" available networks. "Upgrading" the connection to a 4G/LTE network again takes quite some time.

I wonder why the default preferred network is "LTE/TD-SCDMA/UMTS" anyway because there is no TD-SCDMA network in Europe. I think it should be "LTE/CDMA/UMTS (auto) PRL", again, I don't know whether this is part of the problem or just irrelevant.

I noticed this issue mid-January-ish, I do not know whether it can be linked to the Mi Mix 2S' SAR value issue that was discovered by some French authorities around that time ...

EDIT: Same issues with 9.5.9 ...


2019-04-11 22:32:31
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Master Bunny

1634342619 Author | from Mi MIX 2S


Same behaviour today, multiple restarts as a consequence.
2019-04-13 01:27:04

Master Bunny

1634342619 Author | from Mi MIX 2S


Same issue with latest Global Beta 9.4.12, only rebooting /restarting the phone motivates the phone to reconnect with the cellular network ... That's really frustrating. ☹️
2019-04-16 21:54:21

Master Bunny

1634342619 Author |


Being totally frustrated led me to reverting my Mi MIX 2S, M1803D5XA, 8/256GB model, back to the Chinese Beta ROM 9.4.12 yesterday evening, completely wiping the phone and locking the bootloader in the process.

Today, I've tested the "reconnectivity" a few times and surprisingly (?) the phone now works as expected, or at least much better. After completely losing the 4G/LTE connection inside a building (this was also expected) the phone immediately reconnected to the available 2G network and then to the available 4G network upon leaving the building with almost zero lag.

Chinese Beta 9.4.12 comes with baseband version AT4.0.c2.6-303-0409_2210_8fadd5d.
2019-04-18 00:14:50

Master Bunny

1634342619 Author |


url=!AjSrn8DMXuPJnYgWyGWNhveAeD7rQQI've uploaded three examples with modem logs and additional screen shots (MS OneDrive). Maybe someone can make use of the files to create a working and flagship-worthy solution for the issue./url
2019-05-06 20:32:09

Master Bunny

Chan Seng | from Redmi Note 4


2019-05-07 10:32:21

Master Bunny

1634342619 Author | from MIX 2S


4G+ is working. However, the last time I went to Nuremberg I also had to restart my Mi MIX 2S before I could use mobile data and VoLTE via 4G+...
2019-05-09 05:28:29

Master Bunny

1634342619 Author | from MIX 2S


Same behaviour this morning, it's really frustrating.
2019-05-15 14:30:35

Master Bunny

1634342619 Author | from MIX 2S


Here are three screenshots of all the feedback I have sent via the official Feedback app. Does Xiaomi care? No! Again, very frustrating.
2019-05-15 14:33:35

Master Bunny

1634342619 Author | from MIX 2S


To be honest it looks like Xiaomi has improved "something" with 9.5.17... I will do some more tests tomorrow. Maybe Telefónica/O2 (my network provider) becoming an official partner of Xiaomi has helped...
2019-05-22 04:43:43

Master Bunny

1634342619 Author | from MIX 2S


No issues at all today, honestly. My Mi MIX 2S lost the network as expected when I walked from one side to the other side of our workshop, office and social buildings but when I took the phone out of my pocket, it immediately connected to the available 2G network (E) or was already connected. When leaving the buildings or staying close to a window in one of the offices it also upgraded the connection to the 4G network. So, no issues today.

By the way, Xiaomi Mi 9 and Mi 9SE are now officially available through O2 in Germany. Maybe Xiaomi now has implemented the correct network settings for the O2 network in their database/modem.img.
2019-05-23 02:41:00
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