issue properties lost in Jira Upgrade?

[uidev]

Hi,

During a Jira Server or Jira Data Center upgrade, how easily lost are issue properties?:

https://developer.atlassian.com/cloud/jira/platform/rest/v3/api-group-issue-properties/

Would someone need to go out of their way to not include them to be carried forward during an upgrade? Or are they protected along with all other issue data safely? I would like to know for both scenarios: upgrading Jira Server 8 to a higher version, and Migrating Jira Server to Jira Data Center.

I've reviewed all documentation here about common issues during upgrades but would still like to confirm. Because issue properties are "invisible" and not scene from an issue page, an IT member might not check whether they were migrated successfully:

https://confluence.atlassian.com/jiracore/upgrading-jira-server-976161476.html

https://confluence.atlassian.com/adminjiraserver/upgrading-jira-installer-938846937.html