I bought a Ubiquity a few months ago, and found out that it couldn't communicate over wireless with a Raspberry Pi's USB-WiFi dongle (with drivers in mainline kernel) sitting 3 meters away. Before I bought it, the same dongle was acting just fine as access point for the whole home network of 3-4 phones/tablets and 1-2 computers; it could easily handle browsing, updating Android/iOS apps, and YouTube video streaming. And it still is doing that just fine after I sadly had to return the Ubiquity!

Now of course this is just my own anecdote. But it remains a fact that WiFi setup can be incredibly hit-or-miss, and there's no reason in principle why two devices 3 meters away should have occasional 2-3 seconds packet delays.