Samsung Galaxy Tab E Lite WiFi won't stay connected to AT&T Gateway

I just purchased a new Samsung Galaxy Tab E Lite (Model SM-T113)for my son and, during initial set up, it will not stay connected to my AT&T Fiber 1000 internet connection through the AT&T Gateway (Model 5268AC). I returned to the store from where it was purchased, and we were able to get it to connect to the WiFi there with absolutely no troubles. I turned on the WiFi hotspot on my AT&T Cell Phone after that and it connected to that with no troubles. When I connect it to the gateway at my home, it will say "connecting", change to "connected" for less than a second, then the status goes back to "saved, secured". I have connected and disconnected several devices from the WiFi, as there are 2 cell phones, another tablet, and a Roku TV that are connecting to the home WiFi with no troubles at all, either. 

I have attempted restarting the Tablet, restarting the gateway (both hard reset, and by rebooting and resetting using the firmware access). I have tried resetting the tablet back to factory settings, even though I just purchased it brand new. Nothing has worked to change this issue. If it just isn't compatible with the gateway, I will return it, but every other Samsung device I own connects to my gateway with no problems. Any help or suggestions would be appreciated.