Did you go back to the previous version of PennController.js on the project that you shared in your previous message? Because when I open it I still see the old version.
I am still unable to reproduce the issue, but at least one thing that I hoped would have changed with the new PennControlelr.js file is that, even when you see a preloading message, the error message “Uncaught (in promise) TypeError: this.resource.object is null” should have disappeared. Do you still see this message even after replacing the file PennController.js from your project’s Modules folder?
I don’t think this problem has something to do with the software you use for audio compression. I think it might have something to do with the browser’s caching of the zip/audio files. I don’t think it’s related to the server on which the zip file is hosted in any direct way, but it could be that using a different server forces your browser to not use its cache and reload the files instead, which (if my guess is right) would make the problem disappear at least the first time you take the experiment after switching to a different server