Cisco AIR-CAP2702I-E-K9 Controller CAPWAP Association Issue

[Erfan7]

I have hundreds of AIR-CAP2702I-E-K9 installed on different Wi-Fi sites, that are connected to 2 WLC8510 installed on different locations, I have total 3 WLC's 2 WLC's are on 8.5.151.0 software version and 1 WLC is on 8.0.120.21, before the problem my all 2702I series APs were connected to newer versions WLC's, only 1242I were connected to 8.0.120.21.

So it was happened 6 months before, one of my site having 192 AP's suddenly started intermittent with the controller, i.e. capwap was not stable, I did all troubleshooting on both ends(AP's & access side logs etc) but couldn't find anything wrong, then I moved all AP's to secondary Ctrl but issue was stand still, then I decided to move all APs to 3rd controller with older software version and I was surprised to see all AP's are stable for 36 days, now my question is why this has happened although other sites AP's having same model and same image are stable with other 2 WLCs?

[Leo Laohoo]

I make it a point to regularly reboot APs (turning off the PoE and back on).  

This makes them stable.

[Erfan7]

I cant do it on live network, as all APs are under OC monitoring, but all are stable now on 3rd WLC, but I couldn't understand, why this is happening with a particular site even though, before all 2702I AP s were running on same code.

[marce1000]

                >....but I couldn't understand, why this is happening with a particular site even though,

  You probably have to dig into potential intranet-problems, broadcast storms, traffic load , or other, at that particular site

 M.