@diverdown87 

I've been running Deco mesh with M5s at my house since 2020. Mine are US/V3 and I have positive experience of using them. No disconnects. They are currently on firmware 1.6.

Everyone's home network setup is different, of course. You haven't said if your Satellite Deco are wired or connect wirelessly to Main Deco. If they are wired, let me know, there are things to check specific to Deco Ethernet backhaul.

"Other computers wired to the modem do not lose connection when the Deco does" - this tells me you must be having AT&T Fibre gateway, not just modem. The difference is, you can only connect single device to modem and for home network that device must be router. Gateway is modem+router, you can connect multiple devices to it.

As you have tried everything else, there is one more option, assuming you do indeed have AT&T Fibre gateway. It is to set Deco mesh to run in Access Point mode, and disable its SmartDHCP feature. 

See How to set up Deco to work in Access Point mode

Other than turning off Smart DHCP, please keep the rest of settings as they are by default. Beamforming - enabled, Fast Roaming - enabled. You don't need to set static IP address for Main Deco and Satellites - no harm if you did, but I'd rather you not, until Deco mesh is stable.

  @Alexandre. - Thanks for the reply.

Satellites are wirelessly connected to the main one. They are to far away and I do not have a way to run cable to them from the main location where everything is. I have the Arris BGW210 which is advertised as a modem but then again is probably a gateway since I am able to attach multiple devices.

I currently have wired direct to the Arris my desktop PC, the main Deco, and my Android TV box and the only thing I see dropping out is the Deco. The modem is also connected to a TP-Link 16 Port Gigabit Ethernet Network Switch (yes I seem to be a sucker for TP-Link because I also own some of their Powerlines- not hooked up- that the Deco replaced). As I am typing this I have the android box on watching live stream and am answering this on the desktop PC connected to the Arris.

All that being said I will switch the deco back to AP mode and turn off SmartDHCP and swap back to non static IPs.

I will give it some time and see how it goes and report back. Again thanks for the reply and suggestion.

  @Alexandre. As an update, after changing the settings as suggested- it rab fine for about 2 or 3 days that I could tell with no disconnections from the gateway and then returned to same routine of the main dropping connection and killing the satellites. It even did it one day as I was sitting in front of the main and watched it go down, I unplugged it for about 30 seconds, powered it back on watched it reconnect and within 3 minutes it dropped out again. It did this 3 more times. I swapped the main with one of the satellites and reconfigured. Same thing after about 9 hours.

So as of now this will be getting retired to the local e-recycle facility and I will not be recommending this particular set up. It is total junk and was a waste of money in my opinion. I had less problems with the Powerline system by TP-link but hated losing outlets with the ones I had.

Thank you for your assistance anyway. I do appreciate it but I am done with wasting time on trying to make it work stably.

  @diverdown87 

I have the whole cabinet of networking gear that I bought at different times and found it does not meet my expectations. What I do is give that hardware to people free of charge. What does not work for me can work for someone else. In most cases, my giveaways get second life (so to speak) as people using them do not have issues I did.

I understand you do have strong feelings about that Deco set right now, and also spent money on it you can't recover. Still, I would suggest not to recycle Deco set but pack it in a box and put aside. These M5 can run as a standalone WiFi routers, for someone who does not own a router. They can also run as WiFi mesh, and mine do run just fine. You might find someone in a need of a single router, WiFi mesh or add-on to their mesh, or could even gift it to office of some charity. 

It's a waste to destroy Deco set of three M5s, even if you find them of no use for you.

In case I managed to change your mind and you'll keep that set for giveaway, make sure you removed all Deco units from your Deco app, which will force them to do factory reset. See this document for directions, section Reset a Deco unit: How Do I Reboot or Reset My System?