I think you’re going to find details of what’s going wrong and/or not happening in your background tasks log.
A little… erm “background” on that: Analysis runs on your CI agent and collects data about your code. It sends that data to the server in a single bundle at the end of analysis. On the server side the bundle is received, queued, and then processed as a “background task”.
If the analysis happened to be of a PR and if PR decoration is configured, at the end of the background task processing, the DevOps server is contacted for PR decoration. So (as I said - I tend to repeat myself ) its in the logs of these background tasks that we’ll probably find what’s going on.
To find those logs, you must be a project admin. Then from the project homepage, go to Project Settings → Background Tasks. You see all the tasks, most recent first. For tasks that had errors, the cog menu at the end of the row will give you access (IIRC) to the task log. Scroll to the end to find any errors and bring them back here.