On zeroalpha.art we’re seeing occasional failures of requests to https://rpc.xdaichain.com/ :
The response for a failed request:
You can see that the field access-control-allow-origin is indeed set twice.
The request looked like this:
This is something which seems to happen randomly.
The same request usually succeeds (the site polls the state every 5 seconds) - with the response containing only one access-control-allow-origin field (with value set to*).
It looks as if the request is handled by various instances behind a load balancer which behave slightly differently.
