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.
great, thx!
Btw. may it be that the xdai RPC nodes have no min gas price set? Thomas had a tx accepted, but not executed (gas price set to < 1 gwei). If it’s the OpenEthereum client, I suggest to set min_gas_price=1000000000 in the RPC node config.