Hi, I had an issue today where my xwiki stopped working (famous XWiki is initializing (50%)) after I added a table into one of the pages (wiki only has few pages at this moment).
In the server log (HTTP status 500) first root cause was
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Public Key Retrieval is not allowed
Solution - I had to log in to mysql with xwiki user and restart the tomcat9 service.
Helped me, hope it will help someone else, didn’t see an issue like that described yet in reards to xwiki.