Empty means there is the title bar, the footer and in the upper right corner a menu that contains only the title of the Wiki.
Sounds like a new database. You should probably take a look at hibernate.cfg.xml and xwiki.cfg since it does not seems to point to the right DB.
Side note: you solr index is not in a great shape, seems it’s using an old schema. There was a major upgrade in 11.4 that required to delete the solr index and let XWiki recreate it. If you are using the Debian packages the folder to delete is /var/lib/xwiki/data/solr (then restart).
org.xwiki.extension.InstallException: Failed to initialize extension [org.xwiki.platform:xwiki-platform-watchlist-api/11.1]
followed by:
Caused by: org.xwiki.extension.InstallException: Failed to load jar file components
This is for both org.xwiki.platform:xwiki-platform-watchlist-api/11.1 and org.xwiki.platform:xwiki-platform-watchlist-api/11.3
That does not look good, though I cannot think what is causing this.
Removing the solr index seems to me a good idea, too, if only to reduce the number of messages in the log. (Maybe make a backup first, in case you decide to downgrade )
The database settings were OK, but deleting solr folder seems to do the trick. After removing the folder and starting tomcat8 the Installation wizzard comes up and upgrade starts to work.
That should be the folder /var/lib/xwiki/data/solr. Cautions people just move away the folder instead of removing … but normally this is not necessary.
Hint taken from this troubleshooting advice: