why do I have to reconnect devices after wifi goes down and comes back up?

I have only had t-mobile home internet a month now. It has gone down a few times and comes back in a minute or so. But the issue is once it comes back some of my devices are no longer connected. A Epson wifi printer needs to be reconnected by entering the password again using arrows and a list. My TCL ROKU TV needs to reconnect the wifi also. I have had both devices in the same location for 2 years. Neither ever had a problem reconnecting when my century link wifi went down. So why do they loose the connection with T-Mobile?