Could you give more detail about how you setup the OpenVPN server?
By the way, those three AR750, they are in a Site to Site network, but they have same public IP address. Site to Site is for those devices in different location(will have different public IP address).
@Leo is it possible to add a new node to an existing s2s tunnel? We plan to add a lot of devices so it would be great if we can add new devices without deleting and reconfiguring the s2s tunnel?