Slow Wi-Fi after update to tvOS 15

After updating my AppleTV 4K to tvOS 15, my network speeds (as measured by Speedtest) drop from over 500 Mbps to around 100 Mbps (and intermittently much lower). I've rebooted my AppleTV and my network (both my eero Pro 6 and my cablemodem) several times, and have "forgotten" and re-added my Wi-Fi network on the AppleTV.

Does tvOS 15 have a networking bug? Are there other solutions I should try?

Based on my experience and that of others with the same problem who I've spoken with, this was indeed a bug introduced in tvOS 15.0 that had (apparently) been fixed in 15.1 and has now returned in 15.2.