https://confluence.atlassian.com/doc/running-confluence-over-ssl-or-https-161203.html#RunningConfluenceOverSSLorHTTPS-serverconfig
When using a self-signed certificate, it's necessary to also put the cert in the JAVA trust store as well as the tomcat Keystore. We should add something along the lines of:
Add self-signed cert to Confluence JAVA Keystore:

$JAVA_HOME/jre/lib/security/cacerts/keytool -import -alias cert -keystore $JAVA_HOME/jre/lib/security/cacerts -file public.crt

Not doing so can break gadgets and applinks from other applications.

As well the gadget titles per https://confluence.atlassian.com/confkb/internal-gadgets-displaying-titles-as-__msg-935392222.html