I would start looking in to the network for any link specific issue like any CRC errors and congestion in the port where the Netsight server is connected to.
In case if it is sure that the issue is inclined only towards traps then I would recommend to take a TCPDUMP in Netsight while the traps are sent by the switch and that can give a fair idea if traps are received to the server or not.
Once it is confirmed that the trap packet is seen in TCPDUMP and not in the Netsight console trap section, please gather "show support" and open up a GTAC case for further investigation.