Problem:
I was trying to publish a content library externally, so I could access it from a different cluster. However, I couldn't find it. This situation makes me doubt for a while if I really had created this content library, but, I was sure I did. So dude, where’s my content library?

I had to reboot the ESXi (6.7), and the VCSA sited on it for maintenance purpose, and after this, the issue was presented. Investigating a bit more, finally, notice that the Content Library Service never started, it was Stopped.

Solution:
Make sure that the content Library Service is started.
- Access the VCSA via SSH.
- Run the following command to check the Content Library services status.
service-control --status vmware-content-library
- If the service is Stopped, run the following commando to start it.
service-control --start vmware-content-library
- The Content Library Service will start.

After following the steps above, the Content Library should be visible from the vSphere Client.

Other solutions:
VMware can be funny sometimes… if for some reasons you are unable to start the Content Library service, try out this workaround from VMware KB.