Just rereading your description here, is the problem you’re facing on the routed network side? It sounds like (if I’m reading this correctly) if you are connected on the public network that’s assigned to the same subnet as the Stratix you can ping the private side network no problem. However, I soon as you move to a different public subnet you are no longer able to reach the Stratix on the public side.
How are you routing between subnets/Vlans? Have you built the routes on your public network? Is there STP configured on the public network – this has been known to cause some issues if the STP protocols aren’t set to match?