Logging message showing up as nil in online Timber console, but not STDOUT

[dmmcgee]

I am experiencing an issue trying to log with Timber from a Rails application. I am testing locally and have a source set up in the Timber console. Here is my config in initializers/timber.rb:

key = ENV['TIMBER_API_KEY'] || ' '
source = ENV['TIMBER_GCPORTAL_SOURCE_ID'] || ' '

if Rails.env.local?
  http_device = Timber::LogDevices::HTTP.new(key, source)
  Rails.logger = Timber::Logger.new(http_device, STDOUT)
else
  http_device = Timber::LogDevices::HTTP.new(key, source)
  Rails.logger = Timber::Logger.new(http_device)
end

As you can see I am logging to both the timber online console and my local STDOUT.

Take the following log line for example (although I am seeing this with all of my logging attempts):

Rails.logger.info("Malformed payload sent to #{@topic} topic: ", payload: @payload)

When this prints to STDOUT in my local environment, I see this message, which is what I expect:

{"level":"info","dt":"2019-07-29T04:34:44.772889Z","message":"Malformed payload sent to healthcheck topic: ","payload":{"token":"XXXXXX","type":"LAST_WILL","timestamp":"2019-07-28T23:54:06-04:00","body":{"healthcheck_key":"XXXXXXX","sent_time":3109926.657587}},"context":{"system":{"hostname":"Davids-MBP.home","pid":73677},"runtime":{"thread_id":70100616773980}}}

As you can see, the message field reads "Malformed payload sent to healthcheck topic: "

However, when views in the Timber.io console, this is what appears:

Notice the message is showing up as nil.

Why the discrepancy, and how I can get my messages to properly show up in the timber.io online console?