This is a demonstration repo to reproduce appsignal/appsignal-ruby#1418.

In one terminal:

docker-compose up -d # to start Redis
bundle
bundle exec sidekiq

In another terminal start bundle exec rails console and on the console, execute HelloWorldJob.perform_later.

In the terminal running sidekiq, the following log line appears:

{"severity":"INFO","retry":true,"queue":"default","wrapped":"HelloWorldJob","args":[{"job_class":...

However, this line is not forwarded to appsignal: Instead, log/appsignal.log shows

[2025-06-04T13:40:23 (process) #35716][WARN] Logger message was ignored, because it was not a String: {"retry" => true, "queue" => "default", "wrapped" => "HelloWorldJob", "args" => [{"job_class" => "HelloWorldJob", ...

When the job starts, Sidekiq::LogStashJobLogger#call calls Sidekiq::Logging::Shared.log_job which calls Sidekiq.logger.info, passing a simple Hash as input, and that is passed in turn to Appsignal::Logger.add (via Appsignal::Logger.info).

Crucially, Appsignal::Logger.add contains the following section

unless message.is_a?(String)
  Appsignal.internal_logger.warn(
    "Logger message was ignored, because it was not a String: #{message.inspect}"
  )
  return
end

message = formatter.call(severity, Time.now, group, message) if formatter

The check for the message type happens before the message is formatted. This was not always so, the order was reversed with https://github.com/appsignal/appsignal-ruby/commit/cd2f9fbfe31b39de90bc012ddacaaf9b28fef913

The Sidekiq::Logging::LogstashFormatter produces a String, but we never get there.

Reverse the order of the two lines above:

message = formatter.call(severity, Time.now, group, message) if formatter

unless message.is_a?(String)
  Appsignal.internal_logger.warn(
    "Logger message was ignored, because it was not a String: #{message.inspect}"
  )
  return
end