Wifi is connected and has good link and traffic is shown but no IP connectivity possible

Question

I'm getting crazy about that:
iMac 27" Mid 2011, Airport Extrem/Atheros 9380 Core WLAN 4.0 (400.45.1) is connected with approx. 80% link quality (SNR: 45dB, Noise: 1%) to an 802.11n AP with 5GHz an 80MHz with at least 4 other Clients.
The link acts with 270-300 Mbit/s and is pretty good, but sometimes (without any change on network settings or configurations) the IP-connectivity get's lost.
Airport is further connected, traffic counters rise (both RX and TX), while other iMacs (some with similar hardware) are accessing without problems.
How does ist look like:
IP-Address (DHCP is enabled on en1) is bound to the interface and I can ping the local IP-address but NO other IP in LAN (for example the standard gateway).
no ARP requests or broadcasts are shown (except from the local machine)
What did I do for troubleshooting:
created new network location and added new wifi connection
AP reboot
Apple WiFi Diagnostics:
10/29/13 08:35:14.9200
WAN: WiFi interface can ping DNS server 17.254.0.50 . . . pass
10/29/13 08:35:21.9220
No LAN Connectivity
10/29/13 08:35:23.9240
No LAN Connectivity
10/29/13 08:35:25.3650
Scan Cache Updated
10/29/13 08:35:25.9260
No LAN Connectivity
10/29/13 08:35:27.9290
No LAN Connectivity
10/29/13 08:35:27.9290
LAN: WiFi interface can ping IPv4 router 192.168.x.y . . . fail
10/29/13 08:35:27.9290
UNEXPECTED DROP DETECTED!!!
There is no way to use IP communication at this point. The only solution is to reboot or to switch off WiFi an switch on again.
Those problems occure sometimes once a day and another day after every minute!
This is, what wifi.log means at this point:
Tue Oct 29 08:35:25.183 <kernel> scanner_state_suspending_traffic_event state=SUSPENDING_TRAFFIC event=OFFCHAN_SWITCH_FAILED
Tue Oct 29 08:35:25.183 <kernel> scanner_state_suspending_traffic_event retries=02/03
Tue Oct 29 08:35:25.283 <kernel> scanner_state_suspending_traffic_event state=SUSPENDING_TRAFFIC event=OFFCHAN_RETRY_EXPIRE
Tue Oct 29 08:35:25.283 <kernel> HSM: ResMgr :current state BSSCHAN event OFFCHAN_REQUEST[7]
Tue Oct 29 08:35:25.283 <kernel> ieee80211_resmgr_off_chan_scheduler_bsschan_event_handler : Entry
Tue Oct 29 08:35:25.283 <kernel> ieee80211_resmgr_oc_check_and_change_state oc_scheduler_state 0 vap_needs_scheduler 0 
Tue Oct 29 08:35:25.283 <kernel> ieee80211_resmgr_off_chan_scheduler_bsschan_event_handler let the normal bsschan event handler handle the event
Tue Oct 29 08:35:25.283 <kernel> HSM: ResMgr: transition BSSCHAN => CANPAUSE
Tue Oct 29 08:35:25.283 <kernel> 97761.264 | scanner_state_suspending_traffic_entry
Tue Oct 29 08:35:25.283 <kernel> HSM: ResMgr :current state CANPAUSE event VAP_CANPAUSE_TIMER[9]
Tue Oct 29 08:35:25.304 <kernel> HSM: ResMgr :current state CANPAUSE event VAP_CANPAUSE_TIMER[9]
Tue Oct 29 08:35:25.304 <kernel> HSM: ResMgr: transition CANPAUSE => PAUSING
Tue Oct 29 08:35:25.365 <kernel> HSM: ResMgr :current state PAUSING event VAP_PAUSE_FAIL[5]
Tue Oct 29 08:35:25.365 <kernel> 97761.345 | ieee80211_scan_handle_resmgr_events: state=SUSPENDING_TRAFFIC event OFFCHAN_SWITCH_COMPLETE (1) status=00000005
Tue Oct 29 08:35:25.365 <kernel> HSM: ResMgr: transition PAUSING => BSSCHAN
Tue Oct 29 08:35:25.365 <kernel> scanner_state_suspending_traffic_event state=SUSPENDING_TRAFFIC event=OFFCHAN_SWITCH_FAILED
Tue Oct 29 08:35:25.365 <kernel> scanner_state_suspending_traffic_event retries=03/03
Tue Oct 29 08:35:25.365 <kernel> 97761.345 | scanner_terminate: reason=MAX_OFFCHAN_RETRIES pause_requested=0
Tue Oct 29 08:35:25.365 <kernel> 97761.345 | scanner_state_idle_entry
Tue Oct 29 08:35:25.365 <kernel> vap-0: ieee80211_state_event: VAP state event 3
Tue Oct 29 08:35:25.365 <kernel> vap-0: ieee80211_connection_sm_scan_evhandler event 1 reason 5
Tue Oct 29 08:35:25.365 <kernel> ieee80211_notify_scan_done: notifying scan is done
Tue Oct 29 08:35:25.365 <kernel> getSCAN_RESULT: pid[0]:'kernel_task': mySSID (81ms)
Tue Oct 29 08:35:25.365 <kernel> getSCAN_RESULT: pid[0]:'kernel_task': All scan results retrieved
Tue Oct 29 08:35:25.365 <kernel> IO80211ScanManager::scanDone: Scheduling cache purge timer in 30 seconds.
Tue Oct 29 08:35:25.365 <kernel> vap-0: HSM: connection :current state CONNECTED event SCAN_CANCELLED[8]
Tue Oct 29 08:35:25.365 <kernel> vap-0: HSM: connection : event 8 not handled in state CONNECTED
Tue Oct 29 08:35:25.365 <kernel> IO80211ScanManager::getScanResult: All scan results returned for 'WiFi Signal' (pid 10656).
Tue Oct 29 08:35:25.366 <kernel> IO80211ScanManager::startScan: Broadcast scan request received from 'locationd' (pid 96) ().
Tue Oct 29 08:35:25.366 <kernel> IO80211ScanManager::getScanResult: All scan results returned for 'locationd' (pid 96).

Answer 1

Same identical issue and logs for m. expect it says WAN instead of LAN on the failure
Bump, anybody?