I suspect that because this project uses multiple cubemaps,
that they go missing as a result when we download the build
from Play Canvas and host the build on our own server.
We have lots of builds with Cubemaps that are working.
I just downloaded a build myself to host on a local web server and it looks fine to me when I compare side by side to the build published on PlayCanvas
My guess is that your server isn’t configured to serve .dds files or the upload process missed them as they are definitely there in the downloaded build.