Welcome to cayenne community @simplicio and nice work on the cayenne plugin for PLC.
It is nice to see that now PLC data can be displayed on the cayenne.
Just one issue is that what is the time interval for publishing data from PLC to cayenne? This is because you might be hitting rate limit. have a look at this post Sending MQTT messages within rate limits
Also, are you using the same topic for publishing and to subscribe data?