ModBus // Broken Connection

Hi,

I'm using a modbus devices (light,dimmer,ect) with moxa RTUtoTCP converter, the connection is instable and every time give me the message "Error connecting to device", after few second "Device is connected" but if try to change state I get message "Error setting value .... device is not connect ..." After few second the state change anyway but the interaction is very very slow

Any suggestion please?

Thanks a lot