In at least F/W 220.127.116.11 and 18.104.22.168 I a have experienced an intermittent problem of the actual throughput WIFI speed dropping e.g from 8.5 Mbps (our WAN speed) to around 1.0 Mbps. (no neighbouring networks, clients only a few feets away, maximum radio effect). Clients are showing connection speeds of e.g. 65 Mbps and 38 Mbps.
Settings: 2.4 Ghz G/N mixed, all defaults used.
It can be fixed by entering the router and changing e.g. sideband from lower to auto (no rebooting done), so that the router apparently will initialize itself and get up to speed again.
This is, however, in no way a satisfactory solution to the problem.
If the cause of the problem cannot be found an internal watchdog should check and fix it, when it occurs.
I have now created a case at Cisco.
If anybody else has experienced this, it would be a good idea to attach these experiences to the case.