So the root cause is actually:

Caused by: org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: com.xpn.xwiki.doc.XWikiLock#8882132312541106786

I can see lots of different issues in the past related to that same error. Problem is that the information you gave are not enough to reproduce and investigate the bug more.
We would need to understand why the identifier is the same now.
I will close as cannot reproduce as we don't have enough information and the ticket is now old: don't hesitate to reopen if you're still having the issue and/or have more information.