A visitor's switch takes over as spanning-tree root for VLAN 10

At 10:42 every VLAN 10 user in the building loses connectivity for a few seconds. Since then, traffic from servers in VLAN 20 back to VLAN 10 users is slow, and monitoring shows the 1G uplinks of ASW2, a quiet second floor switch, running near 100%. VLAN 20 users see no change. The campus runs Rapid PVST+: DSW1 is root and HSRP active for VLAN 10 (priority 24576), DSW2 is root and active for VLAN 20, and DSW2 has priority 28672 in VLAN 10. An integrator is working in the second floor training room today.