@SJV 

If I suspect the ISP, I connect a PC direct to the modem and see if there is an issue.

When I suspect that a router may be going bad, I would do a factory reset and renter the settings. 

I have found with my Xfinity ISP and surfboard modem that you need to follow the setup instructions for the TP Link routers where it says "Unplug the power to turn off your modem, if any, and remove the backup battery if it has one" when replacing the router. 

As far as the 5GHz WIFI, some things I would look at is the security options on that network, if the router has removable antennas to remove and reattach them, use a different channel, do not hide the SSID (no longer gains you any security, in fact is less secure), and lastly change the SSID and connect one device at a time.  

  @ArcherC8 

I appeciate the suggestions. 

• I have indeed hardwired straight to the modem. No problems with that, though I did mention that after the initial 'outage' all my wired connections remained stable after several modem-then-router restarts. So I have done the router restart sequence about 5 times and 2 modem resets.
• I've never hidden my ssid as yes, I know that is no security benefit. I haven't changed it. I could try that, though if I couldn't get back to the original it would be annoying enough I might just go buy a new router as I have many devices with no interface and I would have to go reset and re-pair them.

I don't see many posts for anything like this newer than 2022/2023, though I suspect most people willing to spend time on a forum are tech forward enough they've already replaced this model with something newer. I just don't want to spend the time to rebuild my whole network.

I did read some answers about cloning the mac address. It seemed to pertain to spectrum as ISP. I also didn't quite understand it, as it read like something out of 1990' (i.e. I only have 1 computer set the mac address of the router to the one device I'm trying to connect with). 

Also, a couple of other weird behaviors here as I've tried to troubleshoot. I have some hard wired devices with IP addresses reserved rather than DHCP. Even with that, as I'm in an SSH session via. Putty into my raspberry pi, it would keep dropping the connection. I could reconnect right away, but I'd get dropped again in short intervals (seconds to minutes). I then seemed to observe a correlation when I had a browser direct connection to my NAS on one monitor and Putty on the other. They'd both drop at the same time, though the browser connection would 'heal itself' while putty would just remain disconnected (prolly nature of putty vs. browser connection).

It seems I'm getting little blips or hiccups of disconnect. This is likely why I am seeing, while in MS Teams meetings I have good quality but experience frequent 2-3 second freezes with warning dialog of poor connection and then it goes right back on and I only missed one or two words. 

I'm just annoyingly trying to figure out if this is hardware or software, and being stubborn about not just going the sledgehammer solutoin of new router (and then days or rebuilding my network device by device).

  @ArcherC8 

Yeah, I've had a WinSCP graphical SSH session going to my NAS up on one monitor and I just see it regularly losing connection and then reconnecting on its own. This probably correlates with the inconsistent responses I get in browser sessions (which is pretty tricky to monitor since not all sites are going to respond the same, but if packets are dropped at just the right time it'll get flakey and it is natural to blame it on the site). 

That or I'm being attacked by the CCP. 

  @SJV 

Do you have any USB devices attached to the router. Test with them disconnected.

Also verify your power. I have seen strange things when the battery in a UPS was going bad. Others have reported home power issues. At a data center I worked at, we got a power dip each time the elevator was used.  Had to use a dranetz meter to track it down. 

  @ArcherC8 

No usb on the router. I don't have a USP or battery backup in my modem. The power is as clean as it can get. 

Good thoughts. The only thing even closely related to that route or major changes I've made is that I added the NAS about 3-4 weeks prior to this problem occuring (or being so obvious?) and that was part of me updating my raspberry pi setup which I use as a Plex Media Server.

I needed more space so upped to the NAS and upgraded to a newer pi and in doing so I used different wiring (used to just have usb storage direct to the pi, now NAS over Cat6 and mounted over ethernet. I was going to start troubleshooting as my performance of Plex diminished in a weird way. I thought there COULD be the possibility I was just creating too much network traffic with that setup vs. the storage right to the pi via. USB. The other thought though  was the NAS software itself might have been at issue as it might be trying to go in low power mode and it was just taking time for Plex on a pi to wake up the NAS as once I finally danced around trying to pull up a show or movie it performed just fine.

None of that should really affect the router much in the way I'm seeing as all of these are hard-wired with a reserved IP addres and the wiring is all Cat6 going through a patch panel in my basement. I mean sure, the route to Internet is from modem to router, but even if Xfinity has a downage I used to and still should be able to have everything humming along nicely on my LAN.

I could test with NAS and pi turned off I guess. Not sure what to test to see if it is making a difference since those were the most problematic items since that 'outage event'. I guess I could try with my Surface 8 on wifi 5GHz and one of my echo's that doesn't seem to want to connect (likely stuck on 5GHz as well).

That is another weird thing I did see. In early testing when I turned off the 5G band, my Surface would still connect to wi-fi but no internet. When I looked at the properties of the connection, it was indicating connected via. 5GHz . This is even after I did a flushdns, reboot, disable/enable the wifi adapter. All strange. 

  @SJV 

I would test check the NAS and PI but like you, I do not think it would be it unless they need more resoures from the router than it can supply. 

I have had a CAT 6 have a broken wire where it reduced the speed to 100 and also had an IP camera that failed at different times because of a bent pin in the Ethernet connector. So you may want to check the Ethernet connectors. Use a flashlight. 

If you have done the factory reset and sill have an issue, next would be to get another router from a place with a good return policy. If it works, you are done. if not ...

  @ArcherC8 

Yeah, a new router is where I'm at now. I turned off the NAS and pi. I Failed to mention I'd already swapped out Cat6 cables in the primary chain in the first troubleshootin round (and made sure the co-ax was tight to the modem) as I've been burned by that in the past.

So i was watching something on Prime video last night on a wired FireTV cube and every once in a while it would throw up a connection error for about 2 seconds (just like my Teams meeting issue). And it was then I realized that had been happening for a couple of weeks as well.

Time to figure out what mesh system I want to go with.