Some times the SM wait 15-18 minutes before skips to next Preferred AP List and show this error in Monitor->Wireless "Failed - SM Network Access Retries exhausted" Version 3.0 ePMP 1000 GPS on AP and ePMP 1000 SM on client.
we did not have any bugs related to INA RETRIES EXHAUSTED in 4.6.2
So the most probably it is a legitimate report. There can be intermittent interference or whatever. Air is unpredictable.
Could you enable spectrum analyzer for 15-20 min on AP and if possible on SM. Then download tech support files and PM it to me. I will try to find some clue.