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 ...
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