There can be several reasons:
Have you completed the full workflow?
A common mistake is to run activation BEFORE the production job is complete.
Did the Jenkins job fail?
If the Jenkins exl job fails for any reason, no content is uploaded to
experienceleague.corp.adobe.com, and no changes are then made when you run activate.
In some cases, an exl job will fail even if the content is valid. Specifically, if there is an outage on Jenkins or Experience League, your production job will fail.
Check to make sure your exl job passes before you run activation.
Do you need to wait a bit longer?
Content is currently scheduled to be picked up for publishing every two hours.
Is there an outage?
Check the sccm-assistance channel on Slack to see if there are outages with either Experience League or Jenkins.
Validation jobs fail due to broken relative links, incorrect syntax, or an service outage.