@smigs Another two possibilities are: 1. Satellite Deco M5 negotiated 100Mbps to the switch, instead of gigabit. This can be tested by wiring laptop to second port of Satellite M5 and running speed...

@aggivatedMAN You can only manage Deco mesh with Deco app installed on smartphone. If someone else configured Deco mesh for you, you'll need to ask them give you access to Deco app. See this TP-Link...

@JoeBlow This is obviously hardware failure. There are no hidden configuration settings to enable/disable 5GHz per Deco unit. TP-Link Support checks this forum during business days in Asia-Pacific...

@NeedHelp0192 If your auntie's mobile device can connect to 5GHz, it should be able to connect to 2.4Ghz. Make that device forget Deco Main Network, connect it to Guest Network and see if lagging...

@GoodWifiForEver This is unusual, indeed. Please re-run speed test, but with the following: Use Ookla speedtest app. Verify it picks same speed test servers at each run; Power off Satellite Deco...

@yoyolele Every Satellite Deco that has Ethernet port can use it for Ethernet backhaul.