Hopefully I'm making this more difficult than it is and/or there is a simple solution.

I'm only going to describe one scenario, but I have others.  A solution to this scenario will help me with all of them.

I use a Smartthings hub strictly to be able to access the Home Control buttons on my Harmony Elite remotes.  The Harmony Home Control button is a Virtual Switch on Smartthings, which in turn triggers IFTTT, which, through ISY Portal, controls a physical Insteon wall switch in my ISY.  Because it is a physical wall switch, it can and will be used too.  Which means I have to synchronize the press of the Insteon wall switch back to the Smartthings hub in order for the Harmony to show the correct state of the light.  I accomplish this through the ISY Network Resources and IFTTT.  It works, mostly.

Sometimes, if I turn the light on and then off too quick with the Insteon wall switch, it goes into a loop.  There is a lag in all of this because of IFTTT.  So if I switch the physical Insteon wall switch on and off too quickly, that is, the off signal is sent to Smartthings before the first on signal from Smartthings has come back, I now have a flashing light.  

I'm not sure if I made this understandable, but I hope so.

In the quick on then off scenario described, I need a way to hold back the off from the ISY from being sent to the Smartthings hub until after the on signal, that will inevitably come from the Smartthings hub, has come through to the ISY.

But why not use Polyglot HueEmulator nodeserver to link ISY control to your Harmony?

Sent from my Pixel 3 XL using Tapatalk

Make the return signal set a variable and run a program to turn the light on.
When the Insteon SwitcLinc sends an Off signal run a program with a Repeat While $sVariable = 0  loop  to make the off signal wait to be sent out until the On is acknowledged.

22 hours ago, Jimbo said:

But why not use Polyglot HueEmulator nodeserver to link ISY control to your Harmony?
 

Oh wow.  How did I not realize that this existed.  Been playing with it the last hour or so.  Fantastic!