Can you use 'Developer tools' plugin to catch the error?
Switch on 'Enable error log' in the plugin's settings and reproduce your issue.
Now check out /admin/develop_tools/error_log
Because the log you provided doesn't clarify the details.
We'll have a look https://github.com/Elgg/Elgg/issues/14842
Will be fixed in the next Elgg release. https://github.com/Elgg/Elgg/pull/14849
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