Have you configured your 'Artnet' port to be the priority - rather than the 'data network'
Go to: system preferences / network settings / config
and ensre that the port you are useing for artnet is at the top of the list as 'preferred' network adaptor.
Try just using one network - rather than both - for what you are doing there will be no speed difference!...
It is possible that serial triggers are being disabled during remote preview mode - dont know if this is a design feature or a bug....
Simon