This is really a cross platform issue as I have 1Password on both Windows and Mac. I'm more comfortable with the Windows file system so I'm posting it here, but also have access to Mac tools if it's easier to resolve there.
So I was using 1Password 6 and I subscribed and upgraded to version 7. When I was transferring my account I didn't know what deleting my original vault meant, but I didn't want to destroy data so I figured I'd keep it and delete it if it was redundant. Turns out, it merged everything into a single vault. So every entry was duplicated in my personal vault and there was no easy way to get rid of the duplicates. And yes, this is all in a single vault - I already removed all local vaults after the transfer.
I tried looking up this issue and found out the Mac version has a remove duplicate tool. I tried using this, but it says "no duplicates found". What?
Fortunately I did back up my vault before upgrading, so I figured I would delete everything in the merged vault version and restore my old vault. Seems like that would work, right? Nope.
I selected everything in my personal vault, moved it to the trash, and emptied the trash. I then went to restore my former database. I verified this vault had no duplicates and moved it to the new vault. This time I wasn't given any dialogues about keeping the old vault. After the transfer I deleted the local vault. Yet it still duplicated everything.
I've been using 1Password since version 1. I've accumulated about 650 entries in my database. The idea of having to clean up duplicate entries manually when it should only take seconds is miserable. Right now I'm regretting upgrading at all. I never had any major issues with previous versions, but 7 is feeling very user-unfriendly. It shouldn't be this easy to screw up or this hard to fix.
Update!!: I finally got this to work by removing all local vaults first and importing only directly into the personal vault. I stand by my statement that this was more difficult to deal with than it should have been.
1Password Version: 7.3.684
Extension Version: Not Provided
OS Version: Windows 10 + MacOS Mojave
Sync Type: Not Provided