I wanted to confirm I’m seeing this behavior as well.
Followed the reproduction steps as described, and then viewed the topic as a user who didn’t have permission to access the category that the topic was set to publish to.
The title of the topic gets displayed over and over again every few seconds until the page is closed.
Without the timer set to publish the topic to a category that the user doesn’t have access to, the topic is displayed as normal (still unlisted).
Discourse Version 2.9.0.beta3
I would expect in this situation that the topic would either be displayed as a typical unlisted topic in the original category that the topic was created in (until the topic is scheduled to publish), or that there would be a message stating that the user doesn’t have permission to access that category of topic.
Certainly a rare edge case, but nonetheless hopefully this information helps resolve this bug.