Build error occurred 1:00:28 AM: TypeError: Cannot add property target, object is not extensible

There’s one known issue that may be causing this but my scenario doesn’t exactly match the associated post: [Support Guide] Netlify app builds locally but fails on deploy (case sensitivity)

Does anyone know if all files must be lower case for Netlify to builds to work? Or is it simply that the references must match the filename?

My application has some files with uppercase, however imports match the case.