HI,
Thank you for bring up this question. Since not able to see any screen shots or detailed logs for this issue, would like to provide some troubleshooting directions to help.
For SPAN Traffic issue.
If not able to see all the traffic for the SPAN session which you've setted between endpoints. Firstly, please check whether your configuration is correct. If yes, secondly, please check whether the span destination port has already reached it's limit and can't take up more traffic.
For packet drop issue.
If you click on the drop button within the Drop/Stats page, you would seen the detailed reason for the Drop Stats. Please check the communication between the endpoint and confirm the ping status between the endpoints. If everything works fine, than the drops could be ignored. But if you've seen some communication issue or anything abnormal related to these two endpoints, please raise a TAC case for further support.
Please check "Getting Started with the Troubleshooting Wizard" part for detailed introduction.
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/4-x/troubleshooting/Cisco-APIC-Troubleshooting-Guide-401/b_APIC_Troubleshooting_4x_chapter_0110.html
