The dropped packets are counted after the filtered packets are disregarded.
There following factors can be reason behind the drop packets:
Packets dropped by the driver due to size exceeding the buffer size. Packets are reported when they are too big (such as jumbo frames) or are bigger than the maximum transmission unit (MTU). To avoid such problems, you can increase Maximum packet size in the Entire Configuration perspective.
Packets dropped due to sampling - controlled drops. Sampling here means dropping packets when the driver performance is degraded. Packets are dropped in a controlled manner, and always with care, to preserve complete and consistent sessions. The packet drops almost always mean that traffic is too heavy for a complete analysis and that, with packet drops, the precision of CAS reports is diminished. Sampling is only active with the customized 64-bit driver and diagnostics always use this sampling mechanism regardless of the settings used in the general AMD configuration.
Packets dropped by the driver due to invalid checksum. Typically caused by insufficient signal strength on an optical link. In other cases, checksum errors may indicate Ethernet distortion, such as duplex problems, where the checksum errors may result, for example, when the duplex auto-negotiation process fails. Check the host switch and AMD duplex settings.
Packets dropped due to performance problems - uncontrolled drops. Drops are always a symptom of problems, especially when SSL analysis is deployed. Drops occur when AMD software is unable to analyze all of the packets it receives from the driver. If you use 32-bit or native drivers, you may experience uncontrolled packet dropping. If you use the 64-bit customized driver, packet dropping may occur, but in a software-controlled manner with care for monitored data contingency. To avoid packet dropping, decrease the traffic volume that your AMD analyzes or reduce the number of monitored software services.
Have a look on the below link for the AMD statistics: