I have seen this before and the problem seemed to come from the Gateway not replying to valid ARP requests. As the vendor couldn't see anything wrong... (even though i had a packet capture to prove it) I forced the customer to roll out a VLAN just for the systems (Which is always recommended anyway) The problem has not reoccured since!

The other issue could be packets 'flooding the CPU' causing the LAN to reset on the SV8100