Hi, as an alternative to dropbox:
I use Resilio sync on two Macs. A free alternative could be SyncThing.
The most important things from my point of view:
Close Publii und the editor you use and give the sync tool time to sync all files before open Publii and your editor on the other system.
I work this way with Publii, Atom and Resilio Sync for several months now without any problems.