"Not found key for dec_ref" when using forward withkeepalive

[luhn]

I recently upgrade to v1.5 and enabled keepalive.

I'm using the fluent/fluentd:v1.5-debian Docker image and my config looks like this:

<match **>
	@type forward
	transport tls
	keepalive true

	<server>
		host "#{ENV["HOST"]}"
		port 24284
	</server>

	<security>
    self_hostname "#{Socket.gethostname}"
		shared_key "#{ENV["SHARED_KEY"]}"
	</security>

	<buffer>
		flush_interval 5s
		total_limit_size 64m
	</buffer>
</match>

When running it, nothing comes across to the destination and on the source I get a continuous stream of errors: [warn]: #0 Not found key for dec_ref: #<Fluent::PluginHelper::Socket::WrappedSocket::TLS:0x00007f64bffed208>

Disabling keepalive resolves the issue.