Node-Red to Espruino

It does look a lot like the echo(0); didn't get through the first time. Perhaps you could somehow dump the code you're sending to Espruino (eg connect 2x USB-TTL modules together, and then listen on one while using the other with Espruino?).

It should be something like:

echo(0);\n

console.log({my:1,json:2})\n
console.log({my:3,json:4})\n
console.log({my:5,json:6})\n

There could also be garbage in Espruino's input line when you connect, so you can try sending Ctrl-C (char code 0x03) before the echo(0) just in case?