Missing communication with plc

You’ll have to give a lot more information to ascertain symptoms:
- communication loss to what device, brief idea of communication link
- what PLC, make model type, brief idea of configuration
A quick search of ' GF A&V300' reveals a stand alone 'behind the glass door' machine, probably part of a larger process,
with it's own PLC and HMI. And Italian.
So the PLC could be one of many manufacturers; with a fault ranging from loss of supply to complete PLC (CPU) failure or anywhere inbetween.