Why is Mongoid/Moped throwing Timeout::Error to Airbrake in production Rake tasks?

Question

I'm having a problem on my production installation. I have several scheduled rake tasks that run successfully. However, I've been getting MANY Timeout::Error: execution expired emails from Airbrake.

But, here's the weird part: the Rake tasks all complete successfully. I'm capturing the stdout/stderr in the cron command, and the errors don't appear in the logs. I've also added simple print statements to the end of the rake tasks to verify their completion.

How can I further troubleshoot this?

Here is a stacktrace from one of the emails:

[GEM_ROOT]/gems/moped-1.2.5/lib/moped/connection.rb:203
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/connection.rb:203
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/connection.rb:235
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/connection.rb:203
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/connection.rb:260
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/connection.rb:260
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/connection.rb:259
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/connection.rb:153
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/connection.rb:30
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/node.rb:507
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/node.rb:122
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/node.rb:527
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/node.rb:542
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/node.rb:526
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/node.rb:515
[GEM_ROOT]/gems/newrelic_moped-0.0.3/lib/newrelic_moped/instrumentation.rb:24
[GEM_ROOT]/gems/newrelic_rpm-3.4.2.1/lib/new_relic/agent/method_tracer.rb:242
[GEM_ROOT]/gems/newrelic_moped-0.0.3/lib/newrelic_moped/instrumentation.rb:20
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/node.rb:70
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/node.rb:376
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/cluster.rb:112
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/cluster.rb:125
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/cluster.rb:125
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/cluster.rb:78
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/cluster.rb:147
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/session/context.rb:108
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/session/context.rb:50
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/database.rb:76
[GEM_ROOT]/gems/moped-1.2.5/lib/moped/query.rb:36
[GEM_ROOT]/gems/mongoid-3.0.5/lib/mongoid/contextual/mongo.rb:69
[GEM_ROOT]/gems/mongoid-3.0.5/lib/mongoid/contextual.rb:18
[PROJECT_ROOT]/lib/tasks/reminders.rake:7
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/task.rb:205
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/task.rb:205
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/task.rb:200
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/task.rb:200
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/task.rb:158
/usr/lib/ruby/1.9.1/monitor.rb:211
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/task.rb:151
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/task.rb:144
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/application.rb:116
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/application.rb:94
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/application.rb:94
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/application.rb:94
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/application.rb:133
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/application.rb:88
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/application.rb:66
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/application.rb:133
[GEM_ROOT]/gems/rake-0.9.2.2/lib/rake/application.rb:63
[GEM_ROOT]/gems/rake-0.9.2.2/bin/rake:33
[GEM_ROOT]/bin/rake:19
[GEM_ROOT]/bin/rake:19