Wow. Haven’t even thought about EuCon devices in a long time. I’ve actually used the EuCon SDK at a previous employer, but I think the last time I used it was 8 years ago or so and the legacy “Artist Series” controllers. Unfortunately their SDK and all of its documentation is all well hidden & requires a login that I no longer have access to.
The connection issue could be in one of a few places:
The EuControl software on the computer may not be listening for control requests on the ZeroTier virtual network interface. I don’t remember if EuControl has a way to configure which network interface its listening on. If it does, make sure to select the virtual network device. On macOS it looks something like feth4788. If you open up the ZeroTier control panel, the device name will be listed with the information about your network as “Virtual NIC Device”
EuCon might need multicast for discovery, and unfortunately there’s nothing we can do to enable that from a mobile device. Multicast is supported by ZeroTier itself, but both Google and Apple do not allow it to be enabled on the adapters the respective OSes give to us.
The control software on your phone/tablet may not be sending packets out over the ZeroTier interface. I’m not sure what, if anything can be done here.