Same here unreachable most of the time..
The network drops to zero for few seconds then come back again.. really irritating..
When phone is locked for few hours then signal drops to zero automatically..very unstable signal reception..
Maybe the Modem config in the firmware are buggy..
Same place Redmi 5a,Redmi 3s same network no issues..
Please fix it ASAP and provide a quick ota update..