To view audit logs for objects in Azure AD you need to have premium licenses. With premium licenses you can view up to last 30 days logs.
If you do not have premium licenses in your tenant then you can view only last 7 days logs.
Were there any operations performed on the problematic user in last 7 days.
You can try to perform any operation like, authentications, password reset, user property edits etc and then you can check the audit logs if you are able to see audit logs.
If you are unable to see the logs, feel free to let me know so that we can work on this issue offline.
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