If you, when you click on Content > Sync status, get an error message, and when you look at /var/log/foreman/production.log, see the below error message:

2016-11-01 19:20:52 [katello/pulp_rest] [E] RestClient.post “https://sat6.FQDN/pulp/api/v2/repositories/search/“, 1613 byte(s) length, “Accept”=>”*/*; q=0.5, application/xml”, “Accept-Encoding”=>”gzip, deflate”, “Content-Length”=>”1613”, “accept”=>”application/json”, “content_type”=>”application/json”
| \n# => 500 InternalServerError | text/html 531 bytes
|
2016-11-01 19:20:52 [app] [I] Completed 500 Internal Server Error in 1047ms
2016-11-01 19:20:52 [app] [F]
| RestClient::InternalServerError (500 Internal Server Error):
| katello (3.0.0.81) app/models/katello/glue/pulp/repos.rb:53:in `prepopulate!’
| katello (3.0.0.81) app/helpers/katello/sync_management_helper.rb:38:in `collect_repos’
| katello (3.0.0.81) app/controllers/katello/sync_management_controller.rb:27:in `index’
| app/controllers/concerns/application_shared.rb:13:in `set_timezone’
| lib/middleware/catch_json_parse_errors.rb:9:in `call’

Then, perhaps, the pulp database did not upgrade properly when you upgraded pulp at some point. Try:

(Running as root)
# usermod -s /bin/bash apache
# su – apache

(Running as apache)
$ pulp-db-migrate
$ exit

(Running as root)

# usermod -s /bin/false apache
# katello-service restart

Done.