This article is about fixing wifi problems, but says it may fix other network issues so it may be worth deleting plist files.
I'm on Sierra 10.12.1beta and can connect to my admin panel ok. Fix Wi-Fi Problems in macOS Sierra
Maybe you found the solution to your problem but there are a few possible solutions. One is that you reinstall Sierra and make the update to latest version. There has been some updates since October.
The other reason that you may not access admin or https sites could be a Global Sign Certificates solution. This can be addressed through Terminal and using the code:
sqlite3 ~/Library/Keychains/*/ocspcache.sqlite3 'DELETE FROM ocsp WHERE hex(serialNum) IN ("040000000001444EF03E20", "040000000001444EF04247");'
Since you are using Time Machine, you can always revert back to the recent backup. As always, there are risks using the Terminal commands...