I've got a dual-sim Galaxy S7 Edge (SM-G935FD) this spring and everything was fine until a week ago my second SIM started to disappear randomly. Basically I wake up the phone after a while and I see no indications of the second SIM: no signal bars and "No SIM card in slot 2" message in settings. Rebooting the phone sometimes solves it for a while -- the second SIM becomes visible and works as expected but after a few hours it disappears again.
Things that I have tried so far:
- wiping out cache partition
- forcibly setting second sim to "2G only"
- manually choosing mobile operators for both sim cards
- swapping sim cards -- problematic sim card would still disappear after a while,
now from slot 1. - putting the problematic sim card into another phone -- it works just fine, not disappearing at all
- factory reset
The issue still persists. Currently my first sim (the one which works well) is set to "auto (4g/3g/2g)", also mobile data goes through that card. My second sim (the problematic one) is set to "2g only", although setting to "auto (3g/2g)" gives same result.
Inspecting phone logs with adb logcat while the second sim is invisible hasn't revealed anything suspicious..
My software:
Android 7.0
ROM: G935FXXU1DQEJ
Build: NRD90M.G935FXXU1DQGN