Thanks burns and I agree the config should be noted. In my case I set parameters 21 and 22 at the switch. I also re-checked my hubitat drivers and they show:
I was having an issue similar to what you described initially. Lights would only work with the dumb switch in one position,not the other. I set parameter 22 at the switch and still no go. But then I set parameters 21 and 22 from my hub to 1, and that fixed my issue.
I was able to solve my problem the same way. It appears that when I included the dimmer in SmartThings it reset those parameters to 0. Once I changed parameters 21 and 22 in the SmartThings app the dimmer now works as expected in a 3-way setup with a dumb switch.
@ragsnova - i seem to be in the same situation as you are, but must be missing something in the app. do you mind elaborating on how you changed those parameters?
I’m having this issue too. Inovelli switch works only when dumb switch is in a certaqin position.
However, I check my parameter 21 and 22 settings in the IDE and they both say 1. I was hoping this was a eureka moment but I guess not. 
I’m using the SmartThings Classic app. Also, assuming you have installed the device handler in the SmartThings IDE. In the app, select the switch/dimmer from the Things list, then click the gear in the device screen. Scroll most of the way down the list to find the AC power type and switch type setting.
thanks @ragsnova, i had the wrong device handler in the IDE.
@Eric_Inovelli/@EricM_Inovelli - this page needs an update for the LZW dimmers.
for anyone else who needs it, they have it in github here.
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I’d recommend setting those parameters again, maybe change them both to 0, then both back to 1.
I set them back and forth from 0 to 1 a few times with no luck. Wish that worked!
Same thing here. Done that several times. Didn’t seem to make any difference and still shows the correct parameters are set.
I’m wondering if just adding a 2nd inovelli to replace the dumb switch solve the problem?
I don’t yet have the RED dimmer. I got involved here as I am planning on adding on in my living room. Trying to help a possible wiring issue I started looking at the details an have come to a theory.
I believe the “Traveler” output of the Inovelli is not providing power as I believe it should.
If someone could test the attached diagrams it would help to clarify where the issue is.
In each I’ve drawn the power path in thicker lines. My supposition is when the Dimmer is “OFF” the light will be off regardless of the position of the “slave” switch.
Conversely when the dimmer is ON the “slave” switch will work fine.
Agree this is a good next step. Have been busy with work and Christmas prep but hope to run this test today or tomorrow. WIll report back with what I find.
OK – spent more time debugging the switch today.
I left it in 3-way config, disconnected the dumb switch travelers, and attached the load directly to the output. The switch still shut itself down when operating the dimmer up or down. While in this wiring config, I rebooted the switch and configured it for load-only. It worked!
I tried reconnecting the load to the traveler line (instead of load) and the switch would not power on.
I rewired it one last time in the original configuation, checked the config parameters for neutral/3-way and tested it. Still failed with dumb-switch in the down position.
I measured voltages on the switch outputs etc. but won’t bore you with all that because… I realized I still had a new red dimmer still in the box. I removed the prior switch, connected the new one, powered-it on, changed config parameters to neutral/3-way, and it works!
SO… the other switch works as load-only and the new switch works as 3-way. These are the same models and should work the same way. The previous switch is therefore “functional,” but there’s something wrong with it that doesn’t allow for proper functionality in a 3-way config. I’ll follow-up with Inovelli.
Closing out this topic from my POV. A properly working switch configured for neutral/3-way DOES work with a dumb switch when wired this way.