Looks like you did not run setup
.
setup sets up the correct mappings, ingest pipeline etc.
Hopefully your are following the steps closely in the Quick start guide
Setup see here
Auditbeat Quick start guide here
If you do not run setup your mappings will not be correct which is what your issue looks like to me.
Also if you Architecture is
Auditbeat > Logstash > Elasticsearch you need to follow this process.
This example is metricbeat but same process
Also I would get
Auditbeat > Elasticsearch working first then introduce Logstash