I disabled my dhcp reservation table and switched to an alternative: (by programming the required ip directly into 21 of the IoT devices, outside of the dhcp pool and started using ARP reservation for said devices)  This seems to help somewhat and (almost) everything reconnects much faster after a reboot. 

The error code 1's have occurred on numerous instances while logging into the router UI, usually by a computer that is hooked up by a LAN cable.  This may not be related, but i'll capture a log file next time i get one. 

While more of my 2.4 devices are connecting and going back online now,  it still appears almost as if the 'smart connect' feature is enabled (it's not) and steering devices away from using the 2.4,  It only seems to happen when the device used is also capable of 5ghz.  Those are the devices that simply refuse to connect to the 2.4 band  (oddly mimicing the behaviour one would expect if smart connect were enabled)

(ex: iphone gets "could not connect to "network-x", or a false 'incorrect password' error.  Android just saves the ssid but wont connect. A PC just times out while trying to connect).  Unfortunatley that is a BIG nusance when trying to connect outdoors where only the 2.4 will reach. (I do have '2.4ghz only' IoT devices which are working just fine outside)

The orignal gateway/router from my ISP (now a NTU)  still allowed all devices to connect to 2.4 while outside, and while its router UI was slow beyond belief,  it did not have these issues, even with the large workload.  

If I add some wireless access points, perhaps one outside,  should that help balance the load?  Can I hook a dual band outdoor AP up to a powerline kit?  (they would still be using the dhcp provided by the c 3150.)   

Problem solved.   Added an outdoor AP driven by a powerline kit.   Fixes 5ghz connection issues and also takes the load off the 2.4ghz on the c3150.  Everything connects and works well now.