Intermittent loss and slow file copies from one wiring closet

Since Monday, users on the third floor say file copies to the file server crawl and video calls break up a few times an hour. Users on the second floor, who hang off the same distribution switch, have no complaints. Floor 3 is VLAN 30 (10.30.0.0/24, gateway 10.30.0.1 on DSW1). ASW3 is a Catalyst 9300 with one 10GBASE-LR uplink over single-mode fiber to DSW1 Te1/1/3. Nothing was changed on either switch.