Upgrading from 5.2.5 to 6.13.20 (I also tried version 7.4.7 initially).
I am able to get the service to start up but when I am unable to access the site and when I look in the logs I see the following in the confluence error log:
02-Apr-2021 22:27:46.895 SEVERE [ajp-nio-127.0.0.1-8009-exec-4] org.apache.catalina.core.StandardHostValve.custom Exception Processing ErrorPage[errorCode=404, location=/fourohfour.action]
java.util.concurrent.CompletionException: com.atlassian.confluence.tenant.VacantException: Confluence is vacant, a call to tenanted [public abstract org.hibernate.Session org.hibernate.SessionFactory.getCurrentSession() throws org.hibernate.HibernateException] is not allowed.