Unable to connect phone and random devices and extener not connecting

[Chaostraveler]

tldr;  Intermittent connection issues with smart devices upstairs, wifi extender randomly disconnects and phone doesn't want to connect due to IP config issues. Issues seem to have been resolved while making post, but I still would love advice.

For some reason, my phone isn't connecting to wifi anymore. I remember this happening a few months ago, but either I never fixed it or something went wrong again as my phone refuses to connect to my router. It says is "IP Configuration Error" and just goes into an endless cycle of attempting to connect. I also have several smart plugs and lights that seem to be having intermittent connection issues, and last night wouldn't connect at all. The other main issue is that my wireless extender that came with the router keeps disconnecting. I notice every month or three it has an amber light under the router connection icon on its front.  I'm never sure how much of a problem this will cause and I never notice any issues with my laptop or consoles when I notice it. 

At any rate, last night I noticed that several of my smart plugs weren't working. As they disconnect and fix themselves every now and then I dismissed it, but saw that the Wifi extender downstairs had an error light as mentioned above. I figured that unplugging, replugging and resyncing to the router would be enough but nope. I noticed that my phone wasn't connected to wifi so I couldn't try resyncing the plugs themselves and resolved to deal with it in the morning. Wake up and smart plugs still have a rapidly blinking light showing they are still disconnected, a quick check shows my phone isn't connecting either. Puttering around I check to see if the firmware is updated, then set up a static IP for my phone just in case (I've had to do this for my laptop and PS5) and finally restarted the router. None of that helped so I started typing this post.

And now everything is working again. I just don't even know what happened. Either with things breaking or getting fixed. I can deal with most minor issues on computers, but networking stuff is not my strong suit. I'd appreciate any advice. Networking and hardware as followed:

Router: Nighthawk XR500 Gaming Router bundled with Extender EX700

Laptop: HP Envy TS 17 something-or-other (look, it's old but it works especially with:) using NETGEAR AC1900 Wi-Fi USB 3.0 Adapter. OS: Windows 10 Home 20H2

Phone: Google Pixel 3 running Android 11

Smart devices: Various TP-Link Smart plugs and 4 Smart bulbs

All of these devices are running on the most recent firmware (or software in case of laptop/phone)

House layout: Router is downstairs plugged into ISP router/modem running in DMZ mode iirc. (I set it up back in March of last year, I just know that I did everything I could to take it out of the wireless environment, including turning off it's wifi.) The extender is set up about 20-ish feet away on a hutch just around a corner from the router. It has some line of sight to the router and seems to be working 90+ percent of the time. Smart devices with issues are upstairs in a bonus room above the garage and top of stairs has line of sight to extender. From halfway up the stairs you can see the main router. Door to my room is 90-degrees away from stairs, yet most of the time things have been working fine wirelessly. Especially with this new router and USB wifi adapter for my laptop.

Thanks in advance for the help.

[Netduma-Fraser]

Are you using Smart Connect for WiFi? Some devices can have trouble switching between 2.4/5GHz automatically and so if you turn it off and connect manually to 2.4 or 5GHz it may sustain the connection. Did you set a static IP for the XR on the modem so the IP doesn't change and therefore the DMZ doesn't become invalid?

[Chaostraveler]

I did not think to set the extender as static, I've just done that. As for Smart Connect, I've been a bit leery about disabling it. I'll likely have to go and reset every single device in the house and then the extender my have it's own SSID to further complicate things. The intermittent disconnect of my smart devices rarely lasts longer than ten minutes, so I haven't wanted to rock the boat. (Well, except for last night. Last night was just really annoying and I had no clue what was going on with all of the stuff in my room except one lamp.)

[Netduma-Fraser]

The extender as static is good, setting the XR500 as static on the modem would be beneficial as well. I can understand that might be a bit of a hassle but it's definitely worth thinking about if it happens persistently, it has helped people in the past.

[Chaostraveler]

Well, now for something (completely) different. Every time I log into my router (I have to go to the gateway ip, I can't use routerlogin.net anymore for some reason) I get an error "Uncaught ReferenceError: start_cycle is not defined" and one of the widgets on the page never loads. On that note, how can I get more widgets or change the theme/color scheme in DumaoS?

[Netduma-Fraser]

Okay so if you can figure out which one it is, either one from the System Information page of Network Monitor most likely then you can go to those pages, unpin them and that will get rid of the error and you can repin it. Most of the panels on the router have a pin icon in the top right of them, if you click that it will then be pinned to the dashboard. There are no other theme/color schemes at present.