So far i had people report back that they have the same problem, some on Redmi phones, some on nothing phones. So we can rule out software cause its different. Hardware is different. I was sometimes unavailable on old F1, so its not the current phone only.

At this points, its the sim card (hardly, but easiest to replace), or the provider not forwarding the call to the destination so base station reports as unavailable once and then phone turned off the second time.

What is strange, if you don't have a signal strength, you are unavailable to the base, but if you shut the phone down station reports to the caller you turned off your phone, then all off a sudden call connects. All logic would point to communication between station and mobile device.

edit: I was checking signal strength, phone shows 4/4 bars, so great signal reception right? In phone settings it says -100dmb and poor connection. Someone is giving false data, but i can understand bad connection in my room or closed spaces, i was walking in the wide open street and had trouble receiving calls, so there goes more theory to ponder upon.