I added a lot of custom meta data on one Mac. After synchronization they don’t appear on my other Mac. Is this a bug or a missing feature? 
@cgrunenberg would have to clarify if this is intentional, but if you haven’t actually used the custom attributes they won’t sync.
Well, I’ve used them on many pdf files. I added them to an existing library from DT2.
The custom metadata of each item is actually synchronized but your personal setup (see Preferences > Data) isn’t. A future release of the sync will probably support this.
Okay, thanks. But how do I access the data? I can’t see the fields in the sidebar.
I just checked this, the synchronization should automatically add missing metadata definitions. Do you use the same versions on both Macs? And did you enable one of the default custom metadata definitions or define your own ones?
I use DT3beta1 on both Macs. On Mac runs Mojave the other High Sierra. I use my own definitions. I even tried to add the missing ones manually (assuming that they are synchronized in background) but then the fields are empty. My files are only indexed and not stored in the dtBase2 folder.
After some days the custom data appeared on the other Mac. It seems I was a bit impatient.