I noticed this about a week ago, but Safari keeps suggesting (and auto-completing) domains with the .co version (e.g., developer.apple.co, youtube.co, bestbuy.co, etc.). This is only for domains that I haven't visited yet. Once I visit the site, it suggests the correct one based on my history. It seems to stop when I turn off "Safari Suggestions" in Safari preferences, so I suspect that's the problem. This occurs on both my Mac and iOS devices. I'm running macOS 10.12.1 Developer Beta 4 and iOS 10.1 Developer Beta 3.
I've tried clearing my history and cookies on all devices, and I've also tried turning Safari sync off in iCloud, but neither of those has solved the issue. Has anyone else experienced this?