As is noted here:

https://developer.atlassian.com/cloud/jira/platform/rest/v3/#api-api-3-issue-issueIdOrKey-changelog-get

When you are retrieving a list of change logs for an issue, the 'items' field has 'from' and 'to' fields that can be used to track changes to custom fields. Currently these return fields are in the form of strings of usernames, not account ID's. It is my understanding these will be removed soon, and with no alternative it will be impossible to track changes to custom fields.

Are there any plans to change this so that account ID's are returned, to allow for changes to be tracked?

Thank you.