This might be a bug I have seen few times. Some login entries contain several websites (URL). If I'm adding the new URL on iOS device, the original URL is overwritten with the new one, creating two line items that are identical. The old URL is wiped out.
The Mac version does not behave this way. There are several reasons I have few URLs for a particular login, for example actual Login URL as well as the main webpage, just for reference.
1Password Version: 6.8
Extension Version: Not Provided
OS Version: iOS 10.3.2
Sync Type: Dropbox