concourse: While watching a job, we get a " You are not authorized to view the details of this pipeline" error

Bug Report

After updating from 5.0.1 to 5.1.0 we’ve observed that when using the UI to watch a running job, then after waiting a period of time (one user reported 30 seconds, I just observed 180 seconds) s the UI shows a 401 Unauthorized - You are not authorized to view the details of this pipeline error message.

Steps to Reproduce

View a running job and watch it.

Expected Results

To watch it uninterrupted by error messages.

Actual Results

Error message appears after 180 seconds (though we’d had varying reports of this time length).

Additional Context

We login to our Concourse with UAA. We have an HAProxy in front of our Concourse.

Version Info

• Concourse version: 5.1.0 - this previously worked fine with 5.0.1.
• Deployment type (BOSH/Docker/binary): bosh
• Infrastructure/IaaS: AWS
• Browser (if applicable): Chrome
• Did this used to work? Yes