2.4 Ghz is a very busy spectrum, and most protocols use some form of collision detect to avoid interference, so it’s probable that the spectrum is particularly busy in that area with the clear line of sight and buildings at four corners. Imagine at least one WAP for every floor times four. And recall that the received signal increases with height. The issue could easily be interference from Wifi devices. And there might be some interference from the other bluetooth radios. There’s also 802.15.4 in the spectrum, which gets used for wireless sensors.
I’m increasingly surprised all this stuff works in that spectrum