Any more details (or links) to share? I read the entire subfolder topic and the only thing Sam talked about was a new alias for Rails in docker
Edit: Did check that long polling is set (no ending slash) per this:
https://meta.discourse.org/t/message-bus-doesnt-respect-subfolder/31119/3?u=jomaxro
Edit 2: No CDN in play here, all on local hardware.