I have a Deco M4R V3 from my ISP (PLDT) in the Philippines and the WiFi recently is way slower than usual. So I tried resetting it and the download speeds and wireless LAN transfers are still slow, but when I got near the unit the speed test is fast again, the problems I encountered are:

The 2.4ghz wifi is pitifully weak after just 2-3 meters away and behind a single wall this isn't usually this bad before so I disabled the 2.4ghz and enabled the 5ghz wifi and it's not showing up on my 5ghz capable phone. I tried turning one of the satellite Deco M4 into the main one and the WiFi problems went away. Anything I can do to fix the broken M4?