@Hkphooey 

Hi, Thank you very much for the feedback.

Did you check whether the wireless speed from the main Deco is also limited to 100m/s?

Please make sure the device is connected to 5ghz, then make sure the wireless link speed is over 100m/s-How to check the associated/link speed on a wireless client

Wait for your reply.

Best regards.

  @Hkphooey 

Hi, have you tried to set Deco as Access Point mode to see whether the speed becomes more stable:

How to set up Deco to work in Access Point mode

And there are two wired devices-- xbox and pc from Deco M4, when the WiFi drops below 100m/s, how about the wired clients and how much do they get?

How often would the wireless speed slow down within one day?

Wait for your reply.

Best regards.