Modbus Poll keeps the connection alive and shows data, but every reading produces an error.
Funny thing: one reading error, one writing error, one reading error, one writing error, ... (even if I'm not writing).
Bonus fact: when selecting "keep connection alive" in the latest teltonika firmware, modbus32 stays alive. For around a minute :| then connection falls. PLC instead cannot communicate.
Bonus fact 2: with modbus tcp slave activated, after startup the RUT955 does not activate the 4G connection! It takes a IP from the mobile network but "no connection" is shown on the connections graph. Only after writing "1" in HR204 (mobile data ON) mobile data start to flow. This happens at every startup.