hi , i have this problem in a few aps.
one is an epmp 1000 without sync ( has only 13 sm registered) , the second one is an epmp 2000.
both are running fine and suddenly kick all SM except one of them (ramdon) . i reboot the ap and can be working for 1 ...3...8 ...10 days without a problem....
today i had same problem.
versions are 22.214.171.124 in EPMP 2000
and 3.5.6 in epmp 1000