Provided Grok expressions do not match field value:

Hi,
I am successfully running filebeats with the logstash module to push serial port logs to elasticsearch/kibana.
However, I get the error "Provided Grok expressions do not match field value:" but haven't set up any grok expressions yet.
Filebeat version filebeat-7.8.0-linux-arm64 running on a Raspberry pi 4b os Ubuntu 20.10 (GNU/Linux 5.8.0-1010-raspi aarch64).

Thanks for your help in advance :slight_smile: