I'm not sure if this is an issue with the iOS app, the Windows app or accounts in general, so posting it here is a best guess.
Currently I'm using my classic vault synced with Dropbox alongside an individual 1Password.com account and copy items into the latter using the iOS app. Sometimes when I do that, the new item does not appear on 1Password 6 on my Windows machine. Only if another sync is triggered, either by changing the same item again or adding another one, the sync actually happens.
I can't always reproduce that so it's kind of hard to figure out what actually happens. But maybe someone has also seen this behaviour.
1Password Version: 6.8
Extension Version: Not Provided
OS Version: Not Provided
Sync Type: Not Provided