I have the SMCD3GN. I have never noticed any major issues with it. I did go through a small period of time where it would reboot often but that's about it. I think I've only reboot it manually about 10 times or less over the last 3 yrs.
Anyway, my issue is that my 1 month old phone (Nokia Lumia 1520) drops wifi connection constantly. When I'm at home I have it set up to automatically connect to wifi. I have an option turned on within the phone to stay connected to wifi after the screen times out. However, I recently hit my 6GB monthly data limit in less than 3 weeks which is something I've never done before. I was able to determine that though my phone shows as connected to wifi it infact is not. And I have to manually disconnect from wifi and then manually reconnect to wifi. If I stop surfing the net or stream media and ut my phone back to sleep my phone will disconnect from wifi within 5 -10 min. If I go back to using it again after those 10 min it will show the wifi on the status bar as active but it will use data until I disconnect and reconnect my data.
I've tried playing with any and every option on my phone possible and have done everything except perfrom and factory reset of the device. I have tried adjusting almost every wireless setting on the router I can. I switched channels, changed the encryption options and rebooted the router. Nothing seems to work. I have found that in the last week my phone did stay connected to wifi on 3 random occassions. I can't point out any reason why those times it worked. I do know that I had to disconnect and reconnect several times before it decided to stick.
Could this issue be with my router? I'm contemplating picking up a $100+ aftermarket router and bridging the two together to see if this fixes my issue. But I'm not confident that this expensive solution is the key to my issue.