MediaLive Channel Preview "Unavailable"

Newbie here, When I deploy MediaLive with this tutorial, I get a working stream up and running normally and without issue: https://aws.amazon.com/blogs/media/awse-quickly-creat-live-streaming-channel-aws-elemental-medialive-workflow-wizard/

When I deploy using template from AWS Solutions Library guide (linked below), I get an error inside the stream Preview player window: "Unavailable. If this channel has recently started, please wait a moment. Otherwise, you may need to restart the channel to enable Thumbnails." The audio however is coming through. Channel has been up and running for a long time, restarting does not help. I would like to understand what is going wrong?

Template download page: https://aws.amazon.com/solutions/implementations/live-streaming-on-aws/