Rpc calls made by web3.js over websockets do not get a response.

I found this issue when trying to benchmark different Hyperledger Besu nodes using Hyperledger Caliper. Our setup is x amount of non-validator nodes behind a dshackle loadbalancer.

When running Caliper we saw that we didn't get any response from dshackle over websockets. When we ran Caliper directly on a besu node everything worked fine. After some further investigation we saw Caliper uses web3.js to make rpc calls. So to test this out we made a small web3 project and found that when web3 tries to send rpc calls over websockets to dshackle it does not get a reply. We do however see the rpc call coming into dshackle (in a grafana dashboard), but the web3 project does not get a reply. When we try to do the rpc calls over https we do get a reply from dshackle, unfortunately Caliper is not able to use anything else but websockets.

Somewhere in the websocket part of dshackle it is not able to send the response to the web3 project.