Seems like this macro is broken in 1.2.4 and the release notes in 1.3.0 and 1.3.1 mention nothing about it.
See related question here:
https://answers.atlassian.com/questions/45530/current-user-macro-not-working-properly?page=1#69641
You could create an issue here https://studio.plugins.atlassian.com/browse/JSUTIL with some more details about the JIRA version in use and what type of custom field you try to put the current user into with that macro.
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