Symptoms

When using the is (dynamic) one of my groups filter on a glide list referencing sys_user_group, the condition evaluates to false if the list field has more than one value

Release

All 

Cause

This is expected behavior as the dynamic filter One of My groups only expects a single reference and when a glide list field has more than one item it would be sending two references. 

Resolution 

You can manually script the condition to check if you are a member of the groups in a Glide List using an array loop.

var currentUser = gs.getUser();
var list = current.my_group_list.getDisplayValue();
var array = list.split(",");
for (var i=0; i < array.length; i++) {

if(currentUser.isMemberof(array[i]){
  return true;
}

}

return false;