Sometimes Content types won’t show up in the Content Type Gallery, for this reason there are some things that you will have to check in just in case:
Check Content Type URL
Sometimes happen that if you change the url of your application web, for instance change it from http to https, you will forget yo change the url from the content type hub.
Check if Content Type Syndication Hub is enabled
Go to Site Settings -> Site Collection Features and make sure that Content Type Syndication Hub feature is enabled
Check if Content Type is Published
Check if the CT is pusblished, also if you are working in a multilingual SharePoint environment, check if you published the CT in the original language of the installation, I don’t know why but it works.
Run Timer Jobs
Go to AC and run the jobs: Content Type Hub and Content Type Subscriber
Check the Content Type Publishing Error Log
Under Site Collection Administration you have a link entitled Content Type Publishing, but inside this link you have another link called Content Type Publishing error log, where is it possible to observe the error that SharePoint are throwing regarding the CT.
Make sure that the Taxonomy Feature is activated for blank sites
Recently I suffered this problem, I created a new SC with a blank template for the site, investigating the issue why the CT were not published in the SC I founded that it was becasue this feature was not activated, so… try it
In last term, run the Content Type Subscriber timer and that’s all
Hope something of this helps someone!