LM bus connection fault

[Domoticatorino]

Drop screenshot of KNX settings and KNX statistics

Hi Daniel,
I unplug step by step some group of devices to verify if problem can be related to some devices in fault. 
In ETS bus monitor nothing strange (max load bus Is 20%) when Siemens Sincos (8 devices) send on bus telegrams   of temperature, status of valves and so on. Consider that facility has only 10 devices connected.

Bus voltage Is 29 volts and there Is no overload on Power supply. But in some case telegrams are not sent. Neither from LM neither from devices on bus. 

Is there a way from LM to monitor the bus voltage? 

Thanks.

BR