I had the same problem with the new DTG ver. 1.5.8.
The issue was resolved after I deleted the iPhone app which also deletes all the data
-> then reinstalled the app and synched database.
Try it out see it works for you.
Regards,
SL
Mac OS 10.10.3 and DevonThink 2.8.5
DTG ver. 1.5.8.