I am new to the use of Let’s Encrypt SSL/TLS Certificate, and I generated a certificate for an Apache Web Server running on Ubuntu Server 16.04.
I observed the home page of my site show “Connection Partially Encrypted” while other sub-domains seem properly encrypted.
I tried to verify with ssllabs and it shows that it was properly encrypted.
It means that an image or other resource was loaded over HTTP, e.g. with <img src="http://www.example.com/...">. You should examine the website and fix it.
https://www.whynopadlock.com/ and your browser’s developer console can help analyze what exactly is being loaded insecurely.