This has started happening to us. Only on certain users, mainly teaching staff. Chrome works for a couple of minutes then becomes unresponsive for about 30 seconds then is accessible for a few clicks then unresponsive. When this happens it usually takes out IE as well. Uninstalled Sophos, moved OUs changed users and rebuilt the affected machines. Usually this cures it for a while but then back into the same cycle. There seems to be no particular pattern to which machines are affected other than it being a member of staff. There are no obvious suspects in the Staff group policies as apposed to the student.