Hi Ilya,
Is there anything in the controller logs? Any mention of anything major going on, any significant interference in the 2.4GHz spectrum etc?
Just to check, are the 2.4 Radios enabled still, and if there are SSIDs unique to the 2.4 spectrum are they still visible?
I've seen this the other way around (on 5GHz when local RADAR caused an issue) but not site-wide for 2.4 unless something has been changed globally.
Assuming the 2.4 radios are still on, are you using auto RF parameters or hard-coded channels and power? Has anything changed there, dropped down etc? Might be handy to look at one of the inventory reports to give you a breakdown of all APs and their 2.4 and 5GHz settings per AP for peace of mind.
Is there an authentication mechanism in the background after the controllers that might be stopping something here? If just PSK, and its an SSID unique to 2.4, has the key changed/still what you'd expect it to be? Could it be a DHCP lease issue (no IPs left, DHCP server problem etc?)
Thanks
Rob
