Xiaomi
Turn On Automatic Network Selection auf Xiaomi
When automatic network selection is off, your Xiaomi phone stops scanning for the best available carrier signal on its own. Instead, it stays locked to whatever network you picked manually, which causes dropped connections after a SIM swap, a firmware update, or when you cross a border and your original operator has no roaming partner nearby.
This behavior is controlled inside the mobile network settings for each SIM card individually. On dual SIM devices, MIUI treats every slot as a separate connection, so you need to open the settings for the specific card that is having trouble rather than assuming one fix covers both.
How to re-enable it
Go to Tap on Settings ➔ Tap on SIM cards & mobile networks ➔ Choose a SIM card (Dual SIM) ➔ Tap on Mobile networks ➔ Enable Automatically select network. The phone briefly drops signal while it searches, then reconnects to the strongest carrier it finds.
Leave manual selection on only if you need to force a specific operator, for example to control roaming costs or stick to a network with better indoor coverage in your area. For everyday use, automatic selection avoids dead spots and saves you from reconnecting by hand after every reboot.