Had a similar issue after upgrading, this command removed the error during squid service restart:
/usr/local/libexec/squid/security_file_certgen -c -s /var/squid/lib/ssl_db -M 4MB
chown -R squid /var/squid/lib/ssl_db/
chgrp -R proxy /var/squid/lib/ssl_db/
References:
http://squid-web-proxy-cache.1019090.n4.nabble.com/Uninitialized-SSL-certificate-database-directory-td4686306.html
https://wiki.squid-cache.org/ConfigExamples/Intercept/SslBumpExplicit