Can't save any Configuration changes post 6.3 upgrade. Dead in the water as Kibana does not remember Default index, etc. and can't set/save same.
(1) Just did a normal sudo apt-get update and upgrade on Ubuntu.
(2) Had to set server.ssl.enabled to true ("Enabling ssl by only specifying server.ssl.certificate and server.ssl.key is deprecated. Please set server.ssl.enabled to true"})
(3) Had to manually remove /usr/share/kibana/plugins ( sudo rm /usr/share/kibana/plugins -r)
"Multple plugins found with the id "xpack_main":\n"