Problem:
Client logon via radius is not possible all at once
Solution:
If this occur in a school environment, you should look for changes in the ucr proxy varibles:
grep proxy/ /var/log/univention/config-registry.replog
e.g:
2018-10-18 11:06:44: unset 'proxy/filter/groupdefault/my-ipad-group' old: unlimited
The internet permission is no longer granted.