Here are a few thoughts, @dkraut.
* Navigate to Metrics > Networks > Click open Capture xx:xx:.... Then confirm you see a row for VLAN 10. If you do, look for clues among the L2, L3, L7 metrics.
* Similarly, if you have the precision packet capture feature, go to Global Packet Capture in the Admin UI and grab a few seconds of packets. Download the result and ensure you see VLAN 10 packets in the mix.
* Automatic device discovery works from ARP packets, so a lack of ARPs coming in along with VLAN 10 could be a factor.