The log shows some:
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 
)