zenaldo wrote Could you kindly let me know what did you do exactly to get the speed back, did you just hard reset all DECO units? I just bought one and upgrade the firmware. My download Wi-Fi using...

Category of 5G channel: Band 1: 36-48 Band 2: 52-64 (DFS channel) Band 3: 100-140 (DFS channel) Band 4: 149-165 Complied with CE regulation, product of EU version supports Band 1/2/3

How do you connect the three Deco units? the main Deco is on router mode or AP mode? how about the other two Deco units? a networl topology would be more clear

If the firmware supports multi-language, you would see the option to change language on the top of the web page, if not, I guess it is a Japanese version and cannot change language...

What is the current firmware version of your router? which one are you trying to download? if the current firmware works fine, there is no need to update

it should be find to open same ports for two devices, your two xbox one have different IP addresses, right?