System Failure due to network problems

MDFB

Hi there, 
I have the following problem: only two IRB 6700 - RW 6.08.01 from more than ten identical robots connected to the same network, entered in a system failure state, aparently after a network loop. After restoring the system, a gap in the event log appeared, and also the only error '20195:System data from las shutdown is lost'.
Someone knows why only two of more than ten robots are having this problem? What differences can be with the others? or what can we do to avoid this? We had the same problem months ago, and not in all robots, after changing network configuration (all device IPs in the network...) .

Thanks in advance!