HSTS Missing From HTTPS Server (RFC 6797)

The missing HSTS response header and command from the web server’s response causes the error and alert “HTTPS Server Missing HSTS” or “Missing HSTS.” HSTS provides end-to-end secure online browsing and website sessions for users. Websites protect users by redirecting them from HTTP to HTTPS. A user may inadvertently use an HTTP link by copying and pasting or manually typing. 

This is something related to IIS and you need to rectified from windows side. Plenty of articles are available which you can follow to enable HSTS on your IIS.