Orbi Slowing Download Speeds

I recently purchased the Orbi RBK50 and have been experiencing slow download speeds. I have looked at many different question regarding this issue, but I have different issues: when I perform a speed test it seems that the speeds are being slowed by the Orbi. I changed settings for the Orbi (disabling QoS, enabling/disabling WMM, rebooting, etc.) and will experience the speeds provided by my ISP (400 Mbps) for a small amount of time. The speed test will occasionally show the expected 350-400 Mbps download speeds, but will commonly display 20 Kbps-10 Mbps download speeds. My upload speeds are normal at 35-40 Mbps upload, but the download speeds are the only speeds affected. Speed tests are performed via Speedtest.net.