IMO it's a hardware fault but DrayTek believe they couldn't find anything wrong. My replacement is nowhere near as bad as the one I had before.

There has been a plethora of firmware updates since this thread was last updated, has anyone had any success with them?

I'm running 3.7.8.3. generally my Wi-Fi is stable, until a Samsung Nexus 10 tablet is used, then Wi-Fi is very unstable for all users.

My last version where correctly works 5 Ghz WIFI is on Vigor2860_v3.7.8.2_STD. I tried Vigor2860_v3.7.8.3_STD, after that Vigor2860_v3.8.1_STD
but always I've had to go back on Vigor2860_v3.7.8.2_STD. Anybody with same experience?

My wifi failed completely all of a sudden 2 days ago. I raised a support call, but found that it worked ok on 5Ghz when I was previously using 2.4.
The support replied saying I should move onto 5Ghz which I had already done. I had upgraded to 3.8.1_STD and that had no effect on 2.4.
It seems to be stable on 5Ghz

on my 2860n the WiFi once completely stopped working. Even applying .RST did not fix.

However, applying .RST, enablign WiFi, disabling WiFi, then applying .RST seemed to fix.

In other words i think something fairly "firm" is toggled inside the router when you enable that checkbox via the firmware interface.

It sounds daft doesn't it, but worth a try anyway...