And what are ther permissions of the parent folder, apmuser? Logstash would need permissions on this folder as well.
User folders have permissions only for the user, you would need to change the permissions of the /home/apmuser folder.
But I would not recommend this, using another user folder for logstash tmp path, you should create a new path like /opt/logstash_tmp, give permissions to the logstash user and use this path as the tmp path.