Often when I use the 1password mini extension to fill a form with CMD+\, or click on the icon and copy a password, I get a spinning wheel in Safari. I had this problem with the released version, so I updated the beta release of both the App and the extensions. It still occurs. I never see this problem when using Chrome.
It will freeze the browser for several seconds, and then it recovers. I can't scroll the page or anything while it's frozen, but it will suddenly scroll the rest of the page when it recovers.
I feel like this has gone on for a long time with 1password and safari. I think I remember it happening in OS X Yosemite as well.
1Password Version: 6.6.BETA-4 (660004)
Extension Version: 4.6.3b1
OS Version: MacOS 10.12.2
Sync Type: Dropbox