On both my Nexus 6p and Nexus 9, sync works after clearing data for the app, but fails every time thereafter. It simply shows the spinning circle for as long as I let it. It works on my somewhat older Windows client if I close / reopen the app. For now, I just copy manually from box and restore, but this is a pain.
As an experiment, I tried again tonight and on Dropbox, the folder for Enpass is created but the sync data file is not added to the folder.
I have the very latest Android version (v6.0.1) with the July 5, 2016 security update on both devices.
Please let us know what the status on this issue is.