Jira 8+ does not run plugin upgrade tasks after the first launch

Summary

Jira 8+ does not run plugin upgrade tasks upon the first launch. After the upgrade, it requests immediate re-indexing, re-indexes the issues, but didn't schedules upgrades to run (in com.atlassian.jira.upgrade.UpgradeScheduler) and didn't execute the plugin upgrade tasks.
The job runs and reports to be finished but plugin upgrade tasks do not run. This will cause problems for plugins that have upgrade tasks (e.g Dev.Status).

Steps to Reproduce

1. Setup Jira 7.x
2. Upgrade to Jira 8.x

Expected Results

The job runs and executes the upgrade tasks.

• example for DVCS:

  2020-01-13 18:17:00,270+0100 JIRA-Bootstrap INFO      [c.a.j.p.dvcs.upgrade.ServiceToHookUpgradeTask_Build01] Running upgrade to migrateHooks /services to hooks
  2020-01-13 18:17:02,241+0100 JIRA-Bootstrap INFO      [c.a.upgrade.core.DefaultUpgradeTaskFactoryProcessor] Upgrade task [factory=com.atlassian.jira.plugins.jira-bitbucket-connector-plugin,buildNumber=1] completed in 1971 milliseconds
  ...
  2020-01-13 18:17:02,509+0100 JIRA-Bootstrap INFO      [c.a.jira.upgrade.UpgradeIndexManager] Reindexing is not allowed after this upgrade and there is no immediate reindex requests
  

• and related logging for com.atlassian.jira.upgrade.UpgradeScheduler

  2020-01-13 18:17:08,486+0100 JIRA-Bootstrap INFO      [c.a.jira.upgrade.UpgradeScheduler] Scheduling upgrades to run in 1 minute(s)
  ...
  2020-01-13 18:18:08,494+0100 Caesium-1-3 INFO      [c.a.jira.upgrade.UpgradeScheduler] Running scheduled upgrades
  2020-01-13 18:18:08,496+0100 Caesium-1-3 INFO      [c.a.jira.upgrade.LoggingUpgradeService] run upgrades has started
  2020-01-13 18:18:09,424+0100 Caesium-1-3 INFO      [c.a.j.upgrade.util.BuildNumberDao] Setting current build number to 805003
  2020-01-13 18:18:09,481+0100 Caesium-1-3 INFO      [c.a.jira.upgrade.UpgradeIndexManager] There are no reindex requests of type [IMMEDIATE, DELAYED] so none will be run
  2020-01-13 18:18:09,481+0100 Caesium-1-3 INFO      [c.a.j.upgrade.util.BuildNumberDao] Setting current version to 8.5.3
  2020-01-13 18:18:09,527+0100 Caesium-1-3 INFO      [c.a.j.upgrade.util.BuildNumberDao] Setting downgrade version to 7.1.2
  2020-01-13 18:18:09,620+0100 Caesium-1-3 INFO      [c.a.jira.upgrade.LoggingUpgradeService] run upgrades has finished successfully, and took 1124 milliseconds to process.
  2020-01-13 18:18:09,620+0100 Caesium-1-3 INFO      [c.a.jira.upgrade.UpgradeScheduler] JIRA upgrades completed successfully
  2020-01-13 18:18:09,626+0100 Caesium-1-3 INFO      [c.a.jira.upgrade.UpgradeScheduler] Plugins upgrades completed successfully
  

Actual Results

The job runs and reports to be finished, but plugin upgrade tasks do not run

2020-01-13 17:09:33,198+0100 JIRA-Bootstrap INFO      [c.a.jira.upgrade.UpgradeIndexManager] Requesting immediate reindex
2020-01-13 17:09:33,870+0100 JiraTaskExecutionThread-1 INFO anonymous     [c.a.j.index.request.DefaultReindexRequestManager] Re-indexing started
...
2020-01-13 17:10:26,462+0100 JiraTaskExecutionThread-1 INFO anonymous     [c.a.j.index.request.DefaultReindexRequestManager] Re-indexing finished
2020-01-13 17:10:26,536+0100 JIRA-Bootstrap INFO      [c.a.j.upgrade.util.BuildNumberDao] Setting current version to 8.5.3
2020-01-13 17:10:26,561+0100 JIRA-Bootstrap INFO      [c.a.j.upgrade.util.BuildNumberDao] Setting downgrade version to 7.1.2
2020-01-13 17:10:26,564+0100 JIRA-Bootstrap INFO      [c.a.jira.upgrade.LoggingUpgradeService] run upgrades has finished successfully, and took 54193 milliseconds to process.

• com.atlassian.jira.upgrade.UpgradeScheduler is not scheduled.

Notes

• jira.upgrade.delay.minutes default to 1

Workaround

• Restart Jira. Jira will run plugin upgrade tasks after restart.
• Trigger the delayed upgrade tasks through REST API: POST /rest/api/2/upgrade
  • see https://docs.atlassian.com/software/jira/docs/api/REST/8.5.5/#api/2/upgrade-runUpgradesNow