Dual SIM not working

we have a iPhone XR where e-sim is ATT and the nano sim is a carrier in China. Our problem is that for some reason, randomly, we lose connection to ATT, restarting it doesn't always resolve the issue. It only works if we remove nano sim from our phone, however, we need both sims.

if anyone have any ideas for possible cause & resolution and is willing to share, it would be greatly appreciated!