I found the problem in a tracker program in our live instance of dhis2 version 2.36.10. Then I tried it in dhis2 play instance of version 2.39 and still found the same bug.
Please see the highlight in blue in the image, it is the actual facility/organization unit of the event which is called by Event UID. But see in the following image, this API is called for multiple events and filtered by TEI. And here is showing the wrong Facility/ Organization unit in blue
Welcome back to the community of practice! And thank you for reporting this bug. Would you like to repost this as a bug issue in jira using your account? (https://dhis2.atlassian.net/)