We got the following error after the upgrade:
Upgrade failed. Please consult the system logs for details. You will need to fix these problems, restore your database and confluence home directory to the pre upgrade state. Then retry the upgrade. Upgrade error message: Upgrade task com.atlassian.confluence.upgrade.upgradetask.ReindexAllBlogsUpgradeTask@3f9afb90 failed during the UPGRADE phase due to: Failed to add entry to queue