When using the Sigma Delta ensure that:
You boot Sigma, control surface and the Remote App before the DAW and Delta Control plug-ins. If at any point Sigma, the control surface or the Remote App is closed/rebooted with the DAW and Delta Control plug-ins open, the system should be booted from the start to ensure proper communication.
The Remote App is open on your DAW PC/Mac at all times in order for Sigma and the Delta Control plug-ins to communicate. This includes situations where an iOS or OSC device is being used to control Sigma.