Keep losing internet connection

So my 27000P is behind an AT&T router. Every couple days, the internet connection is gone, and the only way to get it back is a restart. This is annoying as the kids are all doing school online, and they all come running to me freaking out that they lost the connection. At first I thought setting static IP addresses might fix it, as I noticed this often happens when I turn on another device after everyone else is on. But a tech savvy friend of mine says that shouldn't be necessary. "I have 4 computers, 2 Alexas, 4 phones etc all going day in and day out and I never had to do that." 

I am currently in Router mode. Would I be better of in AP mode? I read the descriptions of both, and at the time Router sounded like it made more sense, but I could be wrong. 

I also have the QoS thing going. Is that actually a detrimental thing? I can easily imagine folks saying, "Oh heck no, turn that off. It's a nightmare." So worth a check, I guess.

Anyone have any helpful input here?

Thanks!

Oh, and I also notice the firmware update check never detects new firmware. It'll say no new updates available, but then if I Google it, there IS a new one, so I've been doing manual firmware updates. I am currently on 1.3.2.126_10.1.66