@Rich - If your Wireless network was running on 9.21.07 for a long time, then recently Access Points started moving, was there some other change in the network that could have altered the traffic dynamics?
@Rod - We are actively working on all reported cases of APs timing out or moving between their respective controllers. If you haven't already looked in the Knowledgebase for Poll Timeout articles, you can try this article:
https://gtacknowledge.extremenetworks.com/articles/Solution/IdentiFi-Access-Points-reboot-due-to-Pol...
However, as you noted above, if there are no outstanding problems in the network, and it is a random AP move, then getting a good packet capture from either the AP ethernet port, or the controller port where the AP's register, could be difficult, but it is a necessary piece to help us understand why the APs are moving.
There are no differences in the timers between version 9 and version 10 firmware.
WASSP packets are already sent with a high priority.