The first thing that comes to mind is that there may be duplicate groups with the same name. Hopefully that is not the case. If there is, perhaps that is why it is returning false. The query finds the first group with that name and unfortunately, you are not a member of **that** group.
See what happens if you remove yourself from a group, then add yourself back in and retry the script. Hopefully it is not an indexing problem, or you are running your script on the instance where you are not part of that group.
Here is a script you can use to get all of your memberships. I modified it so that it will return the names and the sys_id of the group:
var u = gs.getUserID();
var myGroups = getGroupMembership(u);
gs.info(myGroups);
function getGroupMembership(usrID) {
var retArray = [];
var memObj = new GlideRecord('sys_user_grmember');
memObj.addQuery('user', usrID);
memObj.query();
while (memObj.next()) {
var groupInfo = memObj.group.name + '[' + memObj.group + ']';
retArray.push(groupInfo);
}
return retArray;
}
