I’ve reverted to the configuration settings in my original post.
In addition to the 401 error in the Kibana logs that I noted in my original post, I also see the following error in the Chrome dev console when I attempt to create a PDF/PNG report:
Cannot read property 'includes' of undefined
This appears to be the exact same error (word-for-word in the stacktrace) on the front end as issue 5618.
However, in the case of issue 5618, it appears that they couldn’t even create a CSV report, whereas my issue occurs only with PDF/PNG reports. I can create and download CSV reports from the Discover tab or from saved searches in the Reporting tab as expected without any errors in Chrome or in the Kibana logs.