We are also having this problem, for more than one year now. We have 130+ ATVs on campus, PCs with Airparrot and MACs. We are running 6.4.3.7, created a separated SSID, disabled HT, left production with default, but still have a few users complaining about this behavior. I currently have an open TAC and have sent numerous logs, and we have our integrators working with us on the case. We also adopted a few best practices for the devices, that we found to be of influence:
1- the bluetooth communication between devices need to be off;
2- number of SSIDs on APs need to be the minimum possible ( our case is 2)
3- ATVs need to be restarted from time to time (we have gen2 and 3);
4- Macs need to be restarted from time to time.
We also enabled location discovery and active wireless discovery under AirGroup settings, since the MAC OS Airplay does not display more than 99 devices at the same time.
Still waiting on a final answer from Aruba though. Service still seems incosistent, and teachers feel frustrated with frequent disconnections.