Three metres should be no problem for the gigabox unless you’re in an old building and there are some very thick walls separating you from it.
My only suggestion would be changing the wifi channel. I’ve also turned off “Channel Optimisation” as I didn’t want the channel to keep changing.
Both my 5 and 2.4GHz channels are set to auto (currently 112 and 6 respectively) but you could run a network analyser to see if there are any issues. I’ve also read that sometimes bluetooth and zigbee (e.g. Philips Hue hub) can have an impact on 2.4GHz wifi, so you could test turning bluetooth off on your devices and changing any Zigbee channel. Trial and error.
I use Macs, and that has a wireless diagnostics program which can scan and give some info on all the wireless networks the laptop can see. Could be useful.
Or you could just have a faulty box, or you’ve put it in a bad position and are somehow blocking the signal.