title: Mongoid getting no server is available matching preference
body: <p>I have a bunch of sidekiq jobs running that are failing with the following error when I'm trying to perform a query to the DB:</p>
  
  <pre><code>No server is available matching preference: #&lt;Mongo::ServerSelector::Primary:0x70249928071560 tag_sets=[] server_selection_timeout=30 local_threshold=0.015&gt;
  </code></pre>
  
  <p>This seems to happen randomly, and not all the time. My mongoid.yml is structured as following:</p>
  
  <pre><code>hosts:
      - XX.XXX.XXX.X:27000
      - XX.XXX.XXX.XXX:27000
    database: acbde__production
    options:
      connect_timeout: 20
      read:
        mode: :secondary
      max_pool_size: 800
      replica_set: acbdeReplset
  </code></pre>
  
  <p>Anyone had this issue before?</p>