I run all my lights off of one WLED and the others just Synch off of that one. Makes changing light schemes super easy for Halloween, Christmas, etc. But I’ve found if I reboot, the units all go back to the default mode of having Synch turned off. It would be so much easier for me if they just went right back into Synch mode on startup. Surely there’s a way to do this.
You probably didn’t have sync turned on when you saved your boot preset. Turn it on and re-save it.
If that doesn’t work, edit your preset and make sure udpn.send is true.