This is simple case of parser adjusting. Although simple, that doesn't mean it will be quick. I mean what clearly has to be done is verification of
syslog-mail logstash parsers vs actual data from the source. Visualizations might not show data, because parser is not extracting field
You can go to the edit mode and see details of each dashboard panel (which are in fact individual searches and visualizations) to learn details:
Let me know if this helped a little. Here helpful knowledge will be about parsers structures (Input, Filter, Output), plugins and regular expressions. 🙂
I often like to use website https://regex101.com to verify my regexes. Highly recommend.