Unexpected non-whitespace character after JSON at position 93

Hiho, I get this error message since update to NR 4.0x at json node:
"Unexpected non-whitespace character after JSON at position 93"
The message that causes this looks normal to me:

{"topic":"/EspNowPub","payload":"{\"Id\":\"E8:DB:84:9C:22:C7\",\"ESPX\":\"true\",\"MQTT\":\"false\",\"Pub\":\"/EspNowPub\",\"Sub\":\"/EspNowSub\"}","qos":0,"retain":false,"_msgid":"1a57bf5dde0e2ece","_event":"node:6f56b2a5.f434ac"}

On the MQTT Node that generates the message, set it to output a Buffer, then copy the payload using the copy button that appears above the payload buffer when you hover over it.

What version of Node-RED and NodeJS were you on before and what exact versions are you running now?

Lastly, what generates that message?

hi Steve,
I was a bit quick with my post. The message comes from a sensor which is corrupted. The message is forwarded by another ESP Now sensor and I guess that there must go something wrong that I have to investigate.