OnePlus
Select Network Automatically auf OnePlus
When automatic network selection is off, your OnePlus phone stops picking a carrier by signal strength and priority. Instead, it stays locked to whatever network you selected manually last, even if that network is weaker or no longer available.
This setting usually gets changed when you travel and pick a local operator manually, or when the phone fails to register with your home provider and falls back to a manual entry. Switching automatic selection back on tells the phone to search all available networks and connect to your registered home carrier again.
Menu path
Open the Settings ➔ Tap on Wi-Fi & network ➔ Tap on SIM & network ➔ Choose a SIM card ➔ Tap on Network operators ➔ Confirm with OK ➔ Enable Choose automatically
If you have two SIM cards installed, repeat the steps for the second SIM separately, since each slot manages its own network setting.
Keep manual selection only if you need a specific operator for a fixed reason, for example a company roaming agreement. In every other case, automatic selection avoids dead zones caused by an outdated manual entry.