This appears to be a regression.
This can be reproduced by going to ci.blueocean.io/blue in safari, or running a master build from mvn hpi:run - if you click on any pipeline you get a 404 error screen (the pretty one).
When logged in locally, I saw this error from the api:
When not logged in. and trying to open a pipeline on ci.blueocean.io - I saw the same thing.
Seems JWT token related.