Hey @fool - I turned on Asset Optimization after I determined it didn’t make a difference in the outcome for builds.
For what it’s worth, I opened a bug ticket with the build team on the GitHub repo and they mentioned they’d pass it on to the correct team internally: Post-Processing of Custom 404 Page Makes Bundled Resource URLs Relative · Issue #1768 · netlify/build · GitHub
I’ve yet to hear an update, but it would be good to get this resolved.