iOS simulator is a handy tool available for every OS X user but you may encounter This Connection Is Not Private or other strange bugs when using it along some antivirus software.
If you have a problem with running your iOS App/WebApp inside simulator please check if you can establish any SSL connection. In my case it wasn't possible to connect to even https://apple.com.
Open your Avast antivirus program and you should see something like this.
Click on the Settings link under the Disable button and you should see the following configuration.
If you don't know the address or need more universal solution you may uncheck Scan secured connections checkbox but I think that this is less desirable solution.
This solution probably may be applied to other antiviruses which are scanning your SSL secured connections. Fell free to comment if you come across similar problem.
Official Apple forum - https://forums.developer.apple.com/thread/90510