same for me which is why I registered here as this drives me crazy. It worked like a charm in version 5 but since the forced update to 6 there are errors all over. I really question if somone is testing the software as we hear since Version 6.0.1 that it should work now.
With iOS you can somehow sync if there is no vault on the webdav directory yet. Somehow because the sync page says "Last sync at hh:mm:ss" (put any time you want as it is updated every 10 seconds or so). This was not the case in version 5 and it is not if you use iCloud to sync. Beside that it's not working at all if you try to sync with the version 6 PC App from Windows store. There you get an error (either in the Windows App if the iPhone created the vault or on iPhone if Windows App created the vault). I assume that it is not the Windows App as this meanwhile works as expected with webdav sync as long as you don`t try to also add your iOS devices (see above). As said before doing this with iCloud (iOS and Windows) works which is my current workaround but should not be the target as I want to use my OwnCloud setup which is under my control and which was btw. the reason I purchased Enpass.
@Enpass team: Please try to win back credit from your customers in fixing this asap. I guess I'm not the only user which is more interested in stable functionality than in fancy UI enhancements.