N600 WNDR3400v3/Samsung Smart TV Connectivity Issue

Hi. My router has been working fine since I bought it 2017. The last few days, I've turned on the TV to watch Netflix and the connection is fine, but within, say, less than an hour, it disconnects. This happens with 5G and non 5G. I've updated the firmware. 

 

I'm not sure whether the issue is the router or the TV. The internet seems to be working fine, but I need a way to figure out which it is. And then I need to figure out what to do. 

 

Can anyone help? At least with router diagnostics? Thanks!