Had two light switches in my kitchen and either one could turn on and off the lights regardless of the setting of the other switch with no issues.
Replaced one of the standard 3-way switches with a GE On/Off and left the other one in place. Got it all hooked up, it works, it is connected to my hub and works that way and all is golden UNLESS the old switch I left in place is turned off then none of it works. This did not operate that way before.
Is there something I need to do or is this goofiness I just have to live with?
My understanding is that for 3 and 4 way switches you need one of the master switches and all other traveler switches need to be replaced with the GE add on switches.
That is correct. From a very high level, the traditional switches work by rerouting power. The GE Smart Switches have one main switch that turns the light on and off and the companion switches that are put “down stream” that send a signal to the main switch to turn it on and off.
If you did not install the companion switch and only replaced the main switch - you are in essence cutting power to that main switch when you flip the traditional 3-way.
If I install an Add On GE switch, will the behavior go back the way it was (when I could turn or off from either location regardless of the setting of the other switch)?
Depending on your wiring configuration with your 3 ways. Your smart switches won’t operate correctly if the wiring is wrong. Here is a link to all combination of 3 ways configurations. Try to figure out which one is yours first. Sounded like your line in is at one switch and your load is at the other switch hence the need to have the old dummy switch on.
You can’t mix the new GE switch with an existing 3-way wire setup and still have it work like it use to. They are incompatible. The old way is both switches are effectively masters and control the power to the lighting load. The new smart switches do it differently. Only one of the smart switches is the master and it takes the power and controls the lighting load directly. You need a matching GE 12723 Add-On Switch to act as the slave switch (on the GE I believe it will work with up to 4 more slave switches) that basically sends a signal to the master to turn on-off the lighting load. So the wiring on smart switches uses the wiring differently than the existing switches. This setup works like a champ if you want to operate the lighting like you used to.
So if you want to have control from both locations you will need to get the matching slave switch. Or live with the goofyness like you are doing now just leaving the other switch always on providing power to the GE master will work but of course with the limitation from only at the GE.