Some requests to the testReport JSON API endpoint have started hanging, timing out after five minutes. I can send NUnit XML reports privately for someone to investigate and debug. I've restarted Jenkins and the problem persists.

The restReport HTML page works find and returns quickly.

These are multi-branch pipeline jobs.

Requests to https://HOSTNAME/job/JOB_NAME/job/BRANCH/BUILD_NUMBER/testReport/ work fine. Requests to  https://HOSTNAME/job/JOB_NAME/job/BRANCH/BUILD_NUMBER/testReport/api/json hang and time out.

Is there a better way to get tests results via the Jenkins API?