powchain: Could not log ttd status error=json

[come-maiz]

🐞 Bug Report

Description

I am testing prysm+nethermind+mev-boost in kiln following this guide:
https://github.com/flashbots/mev-boost/wiki/Testing

When prysm is running, it prints this error often:

[2022-07-07 03:23:25] ERROR powchain: Could not log ttd status error=json: cannot unmarshal string into Go value of type types.txJSON
got an unexpected error in JSON-RPC response
github.com/prysmaticlabs/prysm/beacon-chain/powchain.handleRPCError
        /home/elopio/workspace/prysm/beacon-chain/powchain/engine_client.go:310
github.com/prysmaticlabs/prysm/beacon-chain/powchain.(*Service).LatestExecutionBlock
        /home/elopio/workspace/prysm/beacon-chain/powchain/engine_client.go:279
github.com/prysmaticlabs/prysm/beacon-chain/powchain.(*Service).logTtdStatus
        /home/elopio/workspace/prysm/beacon-chain/powchain/check_transition_config.go:124
github.com/prysmaticlabs/prysm/beacon-chain/powchain.(*Service).checkTransitionConfiguration
        /home/elopio/workspace/prysm/beacon-chain/powchain/check_transition_config.go:91
runtime.goexit
        /usr/local/go/src/runtime/asm_amd64.s:1571

I'm not sure if this is a problem in nethermind, or in prysm. I'm filling it here to get guidance.

Has this worked before in a previous version?

This is the first time I test this setup.

🔬 Minimal Reproduction

Install and setup nethermind and prysm following this guide:
https://github.com/flashbots/mev-boost/wiki/Testing/f5920c9b000eb0c169c829fe096af7b6793693fb

🔥 Error

```
[2022-07-07 03:29:47] ERROR powchain: Could not check configuration values between execution and consensus client error=timeout from http.Client
github.com/prysmaticlabs/prysm/beacon-chain/powchain.init
        /home/elopio/workspace/prysm/beacon-chain/powchain/engine_client.go:342
runtime.doInit
        /usr/local/go/src/runtime/proc.go:6222
runtime.doInit
        /usr/local/go/src/runtime/proc.go:6199
runtime.doInit
        /usr/local/go/src/runtime/proc.go:6199
runtime.doInit
        /usr/local/go/src/runtime/proc.go:6199
runtime.main
        /usr/local/go/src/runtime/proc.go:233
runtime.goexit
        /usr/local/go/src/runtime/asm_amd64.s:1571
```

🌍 Your Environment

Operating System:

Ubuntu 22.04

What version of Prysm are you running? (Which release)

develop branch, commit b67c885

[terencechain]

thanks for opening this issue @ElOpio, this is a regression in latest commit, we are looking into it