Ruby on Rails

I'm seeing intermittent Postgres errors in my rails app that are resulting in very long-running requests. I've googled this error, but all the results points to a problem with an earlier version of Rails that has supposedly been fixed, or to problems with gems I'm not using (Sideqik) . This is a low-traffic application, and I can't see any pattern as to when the errors occur. 

I'm running the following:

Rails 4.2.1

pg gem 0.18.2

ruby 2.2.0

Postgres 9.1.11, with max_connections=200, current connections ~90

Ubuntu 14.04.2

Passenger 5.0.8

The error is PG::UnableToSend (SSL SYSCALL error: EOF detected)

Stacktrace here.

Anyone have any idea what might be causing this, or how to track down a solution? Thanks!