Users at a branch office complain that a cloud-based application feels sluggish every weekday between 1:00 PM and 2:00 PM, but performs fine at all other times. A technician runs a continuous ping to the application's gateway during the slow period and observes response times climbing from 20 ms to over 300 ms with occasional dropped replies. Interface counters on the WAN router show no CRC errors or discards, but the outbound utilization on the 50 Mbps circuit is pegged at 100% during that hour. What is the MOST likely cause of the performance problem?