Because of HTTPS, Deep Inspection is required
Change SSL Inspection in a policy to Deep Inspection with ADCS
Inspection mode from Flow to Proxy
SSL Inspection from Certificate to Deep inspection
Google, Naver, Daum, youtube, 4shared, Google Drive
Web filter - Unrated should be allowed
Deep inspection
The issuer of this certificate could not be found.
You need to import the root certificate of ADCS
Then, you can correctly access to web
Make Application policy for skype Gmail kakaotalk
then, apply to SSL VPN policy