Serilog machine name enricher for rolling file sink
The machinename and threadid are added as properties to all log events. They are not in the messageformat so serilog does not convert them to a textual representation. They will however be send to the sinks. The Loggly sink will pick all the properties (including the thread id etc) and convert those to something Loggly understands (as it can accept any kind of data).
If you want the RollingFile sink to also output the machinename etc, you need to adjust te output template. So setting it to for example this:
outputTemplate: "{Timestamp:HH:mm} [{Level}] {MachineName} ({ThreadId}) {Message}{NewLine}{Exception}"
See also https://github.com/serilog/serilog/wiki/Configuration-Basics#enrichers
Since the rolling file sink has no way to output all the properties, you only get the rendered message which by default does not contain those properties.