Why does our 5G home internet go out when we are away from home?

Our T-Mobile home internet works well while we are around home with very few problems. But if we are away from home more than a few days, the internet goes out as evidenced by my no longer being able to check on things like Blink cameras, thermostats, and garage door opener. To get it going again, i have to turn the gateway off then on again. What gives? It can go for weeks or months if we are home and using it without needing a reboot. Three days ago, I got a neighbor to go in and restart the gateway and I've been checking it every day and now internet is down again. I suppose I could put it on a timer so the power is cut for a minute each day but not sure that would work since there is battery backup. Any suggestions? If we can't get this problem solved, we may have to switch back to cable which used to be terrible here but has supposedly improved greatly since we switched to T-Mobile.