Usage as Websocket Client fails

Hello,

when setup dshackle as a Polygon Failover RPC, seems to sync fine:

| INFO | Multistream | State of MATIC: height=22251457, status=[OK/3], lag=[1, 1, 0], weak=[]

also a curl works flawless:

curl -m3 -s -X POST -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"eth_blockNumber","id":1}' http://10.1.1.61:8545/poly
{"jsonrpc":"2.0","id":1,"result":"0x15387bd"}

but when trying to access it from a chainlink node, dshackle is throwing:

| WARN | WsFactory$EthereumWs | Failed to proceed with a RPC message: FAIL_ZERO_SUBSCRIBER

and the chainlink node complains about a non functioning rpc provider:

[WARN] Unexpected error while backfilling heads headtracker/head_tracker.go:250 err=fetchAndSaveHead failed: primary websocket (ws://10.1.1.61:8545/poly) call failed: websocket: close 1005 (no status) errVerbose=websocket: close 1005 (no status)

is that a dshackle misconfiguration from my side?

Greetings & thx for this great proxy!