What is Let's Encrypt
Let's Encrypt is a free, automated, and open Certificate Authority.
Why do the certificates only last 90 days?
Due to the automated nature of Let's Encrypt, the certificates have 90 day validity.
If the certificate expires - You can reissue in cPanel - This is called domain valided SSL and to prevent security issues - The validily is shorter than EV - Paid SSL
What is the difference between Let's Encrypt Vs Other Paid SSL
Domain validated or DV certificates are the most common type of SSL certificate. They are verified using only the domain name
Extended validation or EV certificates provide the maximum amount of trust to visitors, and also require the most effort by the CA to validate
Ev certificates normally require dedicated IP address to bind the certificate