Persistent "Network request failed" Error in UXP with HTTPS/ELB Endpoint

UXP Developer Tool
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My Photoshop UXP plugin is blocked by a generic “Network request failed” error when calling my AWS ELB endpoint.

  • The key issue: The same fetch code succeeds when calling a public HTTPS test endpoint (e.g., jsonplaceholder.typicode.com), confirming my manifest.json permissions and UXP environment are fundamentally working.

Since the error only occurs on my ELB, I suspect a problem with the SSL certificate chain on the Load Balancer itself, as UXP seems to be rejecting the connection pre-flight. Has anyone seen UXP reject a valid connection only from a custom AWS ELB before?