It appears that LogStash doesn't like hyphens or something?
These are IIS logs by the way. I get this error in my date field:
[2019-05-28T16:35:58,176][WARN ][logstash.codecs.jsonlines] JSON parse error, original data now in message field {:error=>#<LogStash::Json::ParserError: Unexpected character ('-' (code 45)): Expected space separating root-level values
at [Source: (String)"2019-05-27....(data)....line: 1, column: 6.....(data)....
Column 6 is the hyphen after 2019. Any ideas?