A look into Debug logs might help. From Administer::Diagnostics, enter an Android device MAC into the box, and check 802.1x and Client Association debug components.
After a period of time, when this User has/reports a problem, save the Debug Logs (and the Support Info from the AP they were on if known, from Monitor::Access Points).
Share these with our support team and we may be able to get to the bottom of the connection issues.