Is there a bug in 2021.3.1f1 WebGL builder files?

I've a game that was working fine in older versions of Unity. I upgraded to 2021.3.1.f1LTS, built the game, uploaded it, and it will not load. I'm getting this in the console: https://learningchicken.com/JBN/Config_and_E_Chicken/Build/WebGLbuild.jpg.unityweb [HTTP/2 404 Not Found 925ms]

Failed to load 'https://learningchicken.com/JBN/Config_and_E_Chicken/Build/WebGLbuild.data.unityweb' from indexedDB cache due to the error: TypeError: Error in body stream WebGLbuild.loader.js:1:15692

Is this some error in the build where something is being requested by the index or the build that isn't in the build directory or do I have some bad interaction with my server?

EDIT: What is not getting downloaded appears to be the background image for the loading screen. EDIT:It is also failing when creating a new blank project, setting the background image, and building and running from the HD, so its not a problem with my server (whose error log is empty)