New User - Sync Issues?

Hello - I am new to Bright Sign and have a possible issue with Sync. I have 2 HD1010 units. I have successfully created projects using Bright Author on both of them, and added UDP control. They work fine. I now want to add some synchronized videos. I watched the demo video, and followed it. I created a project for the master unit, using the synchronize command. I did not use a timeout event, but used a UDP event, as I need to trigger this externally. On the slave unit, I added a synchronize event, and entered the same keyword as I entered in the command on the master. I still have UDP event to trigger videos individually as well. When I run these projects, the Master is still controllable via the UDP events, but the slave is not. When I try to run the synced event, nothing happens the first time I send the UDP command (to the Master only, of course) that triggers it. If I send that same UDP command to the master again, the video runs on the master, but the slave does nothing. If I take that same project from the slave, and remove the synchronize events, it goes back to working for UDP control as before. It seems that when I add the synchronize events on the slave, it stops taking UDP commands. Am I doing something wrong? I need to be able to trigger indiviual videos on the master and the slave, and then at certain times, trigger a synched video that plays from both of them. Any help would be very appreciated. 2 - HD1010 units Firmware 3.5.77 BrightAuthor 2.2.0.39 Thank you!