Error "No upstream pool ID was found for Katello::Pool with ID: XXX" is displayed on the subscription page of Red Hat Satellite 6.4

Issue

• In the Satellite Web UI, the following error message is displayed:

  No upstream pool ID was found for Katello::Pool with ID: XXX"
  Also one or more subscriptions checkbox is grayed out and cannot be attached to anything. 
  

  Log File : /var/log/foreman/production.log
  
  2018-10-26T08:35:41 [I|app|edc0e]   Rendered /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.7.0.41/app/views/katello/api/v2/subscriptions /index.json.rabl within katello/api/v2/layouts/collection (1611.4ms)
  2018-10-26T08:35:41 [I|app|edc0e] Completed 200 OK in 1965ms (Views: 1597.9ms | ActiveRecord: 47.3ms)
  2018-10-26T08:35:41 [I|app|] Started GET "/katello/api/v2/organizations/3/upstream_subscriptions?organization_id=3&pool_ids[]=106&pool_ids[]=46&  pool_ids[]=96&pool_ids[]=108" for 1.2.3.4 at 2018-10-26 08:35:41 +0200
  2018-10-26T08:35:41 [I|app|021e9] Processing by Katello::Api::V2::UpstreamSubscriptionsController#index as JSON
  2018-10-26T08:35:41 [I|app|021e9]   Parameters: {"organization_id"=>"3", "pool_ids"=>["106", "46", "96", "108"], "api_version"=>"v2"}
  2018-10-26T08:35:41 [I|app|021e9] Current user: doerflt (administrator)
  2018-10-26T08:35:41 [E|app|021e9] RuntimeError: No upstream pool ID was found for Katello::Pool with ID: 106
  /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.7.0.41/app/services/katello/candlepin/pool_service.rb:16:in `block in local_to_upstream_ids'
  /opt/theforeman/tfm-ror51/root/usr/share/gems/gems/activerecord-5.1.6/lib/active_record/relation/delegation.rb:39:in `each'
  /opt/theforeman/tfm-ror51/root/usr/share/gems/gems/activerecord-5.1.6/lib/active_record/relation/delegation.rb:39:in `each'
  .
  . [ output omitted ]
  .
  /usr/share/gems/gems/passenger-4.0.18/lib/phusion_passenger/rack/thread_handler_extension.rb:77:in `process_request'
  /usr/share/gems/gems/passenger-4.0.18/lib/phusion_passenger/request_handler/thread_handler.rb:140:in `accept_and_process_next_request'
  /usr/share/gems/gems/passenger-4.0.18/lib/phusion_passenger/request_handler/thread_handler.rb:108:in `main_loop'
  /usr/share/gems/gems/passenger-4.0.18/lib/phusion_passenger/request_handler.rb:441:in `block (3 levels) in start_threads'
  /opt/theforeman/tfm/root/usr/share/gems/gems/logging-2.2.2/lib/logging/diagnostic_context.rb:474:in `block in create_with_logging_context'
  2018-10-26T08:35:41 [I|app|021e9] Completed 500 Internal Server Error in 10ms (Views: 0.2ms | ActiveRecord: 1.6ms)