My unlocked s21 ultra has dual sim, from the settings, I chose sim 1 to be my data + calls + sms, however when you enter a building garage... The phone changes the data sim from sim 1 to sim 2... Why?
I put a limit on data size for sim two, it still uses it randomly, so I turned off sim2, now it can't find data after visiting a building garage, and you have to manually change from nothing to sim 1 data...
Note 10 had the same problem... Help
