intermittent service broker send blocking issue

We have noticed that we occasionally see long running blocking issues when sending concurrent service broker messages via SP. The blocking was traced back to the following system object : "queue_messages_368720366".

Here is the snippet of tsql send code from our sp that encounters intermittent blocking issues (longer than 30 seconds):

If (@MessageBody IS NOT NULL)
BEGIN
		SET @Handle = NEWID()
		BEGIN DIALOG CONVERSATION @Handle
		FROM SERVICE ImageAuditPublisher
		TO SERVICE 'ImageAuditSubscriber'
		ON CONTRACT [http://schemas.foo.com/contracts/ImageAudit]
		WITH ENCRYPTION = OFF;
		SEND ON CONVERSATION @Handle
		MESSAGE TYPE [http://schemas.foo.com/messages/ImageAudit/Insert](@MessageBody);

END

What would cause "queue_messages_368720366" to experience intermittent blocking issues?  too much load?

Microsoft SQL Server 2014 (SP1-CU3) (KB3094221) - 12.0.4427.24 (X64) 
Oct 10 2015 17:18:26 
Copyright (c) Microsoft Corporation
Enterprise Edition: Core-based Licensing (64-bit) on Windows NT 6.3 <X64> (Build 9600: )