Generated by Spark: The usual culprit (90% probability)

VITE_BASE_URL / VITE_PUBLIC_PATH (or equivalent)

Many templates do this in vite.config.ts:

base: import.meta.env.VITE_BASE_URL,

or:

base: process.env.VITE_BASE_URL,

If that variable:

is undefined

defaults to /

or was set to http://localhost:5000

then Vite bakes the wrong paths into the JS bundles.

nginx then serves files that point to nowhere → flaky load.

vite.config.ts

@@ -10,6 +10,7 @@ const projectRoot = process.env.PROJECT_ROOT || import.meta.dirname
 
 // https://vite.dev/config/
 export default defineConfig({
+  base: './',
   plugins: [
     react(),
     tailwindcss(),