Depending on your network infrastructure, you may be required to increase the wait time for SNMP timeout or increase the number of SNMP query attempts. Conversely, if your network speed is optimal, you may be able to shorten the SNMP timeout.
SNMP Timeout - This setting is the number of milliseconds Subnet List should wait for an SMNP reply before assuming the packet is lost and trying again.
SNMP Retries - Designates the number of times Subnet List should retry an SNMP query before considering the device down. Set this to two or higher.