The seemingly pyramidal mystery turned out to be a feature: a GSM modem for sending SMS messages was connected to the IPLC300 in the previous application on COM2. The application was later ran by a new program that COM2 used to integrate heat meters via M-Bus, however, the configuration file remained in the controller and tried to establish a connection to COM2 with the GSM modem, thus preventing communication via M-Bus.
Therefore, when using the controller for another application, do not forget to delete all configuration files for GSM (Messaging definition) and Modbus server using the cross buttons in Platform Config.
