Our daughter told me of WiFi dropouts and slow speed on her gaming PC. I replaced the WiFi adapter and dropouts ended but I saw speeds were only ~80Mbps and should be much higher. After rebooting mesh nodes and fiddling settings to no avail I discovered even some Ethernet connections were only 80Mbps.
Long story short there was a flaky Ethernet cable in my study which somehow caused all this. After replacing it even the AppleTV is getting download speeds over 900Mbps. No comprende.😖