Samsung
Select Network Automatically auf Samsung
Samsung phones pick the strongest available network by default. That changes as soon as you choose a carrier manually from the network list, for example while roaming or troubleshooting a weak signal.
Once a manual selection is active, the phone stops scanning for a better network on its own. This can cause dropped calls, slow data, or no service at all once you leave the coverage area of the carrier you picked.
Where to switch it back on
Automatic search sits in the mobile network settings, right next to the manual carrier list. Follow this path:
Tap on Settings ➔ Tap on Connections ➔ Tap on Mobile networks ➔ Tap on Network operators ➔ Enable Select automatically
After enabling it, the phone searches again and connects to the best available network for your SIM. This usually takes a few seconds.
If Select automatically stays greyed out, turn on mobile data first or restart the phone, since the toggle needs an active mobile connection to run the search.