@Richj44 

To me, this appears to be an Interference problem?

In the Deco App, you can Optimize the Network... and it will swich frequencies on the bands if it detects interference or weak signals.

When you installed the Deco's, and removed the Orbi System, did you turn off the Modem before installing the Deco's? Once the maiin Deco was powered up, then turn on the modem? Modem's hold info about the last connected device and 'hot plugging' a new device (PC, Phone, Tablet) to the modem can have connection problems.

Since it is all devices, either the main Deco or the connection to the modem would be the problem.

Another thing to try then, switch the Deco connected to the modem. If that Deco was causing the problem, all the others would have it too, but if it is the problem, one of the other Deco's might work fine for devices connected to it and the other Deco as well. Problem would then be only on devices connected to that Deco that was the main one before.

If it still happens, I'd be looking at the Modem causing it?

  @IrvSp Thank you for your suggestions.  I ran the Optimize Network tool multiple times.  About twice it made some changes, about a dozen other times the scan came back "Perfect".

Yes, I followed the installation instructions and shut down my modem before swapping to the Deco.  I've also rebooted everything in the network multiple times.  It hasn't made any difference.  The only one of your suggestions I haven't tried is swapping which device connects to the modem.  At least, not intentionally.  At one point I ripped the decos out and set up the Orbis again to see if the problems persisted and nope, they did not appear with the Orbi.  Rock solid like always.  That's when I reinstalled the Deco system, this time setting them up as an AP rather than a router option. I didn't mark which one was connected to the router before, so odds are I connected a different one but I don't know that.  Regardless, the problems came right back.  

I'm afraid I can't see how the modem causes the problem if the problem vanishes when I use the Orbi system in the same configuration with the same modem.  But I do appreciate the suggestions.  However, the Deco is back in the original box and will be dropped off at UPS in a couple of hours.  This was mainly a gripe post I'm afraid, not a troubleshooting attempt because I'm satisfied with the troubleshooting I've done and convinced it can't be fixed.  Maybe I got a buggy Deco system, or maybe my smart devices just don't like something about it, or maybe the moon is in the wrong phase, I don't know.  I do know I don't want to deal with the frustration when I can solve the issue by switching back to Orbi, so that's what I've done.  Have a great day!