See MQTT 2.5 M1+ How to implement the equivalent to MQTT1 REGEX filters. Set REGEX expression to look for something that identifies that the message contains the JSONPATH value. Only if the expression matches will the message be passed to the JSONPATH, eliminating the errors.
Another option is to use the Shelly binding. It’s still local control but handles all this stuff for you.
You can change the log level of the whole binding using org.openhab.binding.mqtt
But the expected way to handle this is through that REGEX filter.