There is a serious UI bug that can potentially make all items inaccessible. I can reproduce it the following way:
In my case there are no duplicate passwords to show. So the resulting list is empty. However, for some reason the dropdown box is now greyed out and no longer clickable as can hopefully be seen in this screenshot:
I tried clicking around various places in the UI but the dropdown remains impossible to click. The result is that none of my items are now shown in the Logins category.
I did actually manage to get it working again by typing something in the search field and then selecting something else in the dropdown. But there is definitely an issue with the UI that needs to be fixed.
1Password Version: 6.3.5
Extension Version: 22.214.171.124
OS Version: 10.12.1
Sync Type: Account