Re-boot

Not sure if this is your case, but here's a possibility. There's some guesswork and assumptions I'm making about how the service works.

When you reboot the gateway, I believe it will search and lock on to the fastest/best band/tower connection it can find at the time. If during the day that connection degrades or disconnects, the gateway will switch to a different tower or band. As long as that new connection stays stable it will stay with it even if the better band/tower becomes available again. The only way to get back to the ideal band/tower is to reboot assuming the preferred band/tower is available, of course.

I occasionally have issues with the 4G (Primary) Signal switching to a different band/tower. This is usually only a minor problem though. But, a few times, I've noticed my 5G (secondary connection has switched from the n41 band/tower to the n71 one which is much slower. When I reboot the gateway it goes back to the best signals.

So, before you reboot next time, open up the T-Mobile Home Internet app, select the "MORE" tab, then "Advanced Cellular Metrics". Take note of the information for both the LTE and 5G signals. Then once you've rebooted, check the metrics again and see if there's a substantial difference and if the band is different. There are discussions throughout this community about what the metrics mean.

If it is switching and it's a constant issue for you, you may need to contact T-Mobile and see if they can do anything about it. Good chance they'll just tell you they are "working on the towers" so be prepared for that.