noted on the SEP, this could be the reason.
Is this wired or wireless that you're seeing the issue? - wired
Are the NIC drivers up to date? - it should be up to date though not the latest
Are you seeing similar issues with Macs?- not using macs
as for the sometimes no radius authentcation issue, i can see from the switch that the client is 'authenticating' however after awhile it fails, and i don't see any log from the access tracker. as mentioned i don't see this behavior very often, i am just wondering what could cause such issue.
i also have another issue where machine authentication is not being triggered upon log out. this behavior also happens sometime. only upon rebooting the machine, the machine auth is being triggered.