Having a couple of issues out of the blue for some reason...

[Landonio1]

So I haven't really had a major Netduma/internet problem in a while, but recently it's been acting weird. And I don't really know what the deal is. A couple of weeks ago, my wi-fi was dropping out for extended periods of time for seemingly no reason. Not only that, the Netduma would completely disappear from the list of available networks. The LAN connection however is fine. I have my PS4, Series X, and PC all connected via LAN and never have an issue. Also my NAT is still showing "Open" on my consoles, so no problems there. If I reset both the modem and router, it returns to normal. But then a few days later it will do the exact same thing. After about the 3rd or 4th time it happened, I went into my modem (it's a Pace 5268AC, fyi) to see what I could find. Lo and behold, somehow the wi-fi on the modem was kicked back on. I turned it off years ago. I never changed a single thing since, so I have no idea how this happened. And because of that, there was no password anymore, so I saw what appeared to be the entire neighborhood leeching off my Pace's wi-fi. I assumed this was the issue, so I disabled the wi-fi on the Pace again, reset everything, and the issue seemed to be resolved. But it just happened again for the first time since then. I double checked to make sure the wi-fi didn't get kicked back on again, and it didn't. It's still disabled (but what's weird is it's still showing 2 unknown devices connected to it, which is impossible because the wi-fi is disabled). So I'm kind of at a loss again. On top of that, I also noticed that I'm getting that message on the Netduma about "being connected to another router"  and to "enable DMZ", which I already have done for the Netduma. That's never changed. I haven't gotten this message in like 2 years. So something's up. No idea what to do. Any help would be greatly appreciated. My OS is 1.03.6h btw, if that matters.

I also have a couple of other miscellaneous questions. 

1. DCHP lease under "LAN". Mine is set to 12 hours. Should that be lower? Higher? Not sure about that.
2. IPv6. I asked about this a few years ago. But with the new consoles out and everything,  I figured I'd inquire again. Should I still keep this disabled? Or will it be better to enable it for the new consoles?

3. I noticed that my modem has "HomePNA" enabled. Should I disable that? I don't even know what that is. 
4. Any other things I need to modify or adjust to prevent issues or just to have the optimal experience with the Pace as the modem for the Netduma?

[Netduma Liam]

Thanks for the great detail, that's really helpful.

The first thing I'd note is that you're a little behind on the firmware, I'd suggest an update to the latest: V.2.1.3.29. I'd also advise performing a factory reset after this to clear any low level code still hanging around.

To be clear, is the R1 in the upstream modem/router's DMZ? 

To answer your questions:

1. I'd advise setting the DHCP Lease time to 168 hours, this may be related to your issue.

2. I'd advise keeping it disabled personally, but feel free to give it a try, just make sure your ISP supports it!

3. I've had a little look and it appear this is a technology for allowing devices to communicate within your network over the telephone lines. If you're not using it, might as well disable it!

Let me know if these things help with your issue, we can then dive in to further troubleshooting if not!