Hello,
Nintex rules become active when they are returned a value of true based on their evaluation.
Logical AND (&&) expr1 && expr2 Returns expr1 if it can be converted to false; otherwise, returns expr2. Thus, when used with Boolean values, && returns true if both operands are true; otherwise, returns false.
Logical OR (||) expr1 || expr2 Returns expr1 if it can be converted to true; otherwise, returns expr2. Thus, when used with Boolean values, || returns true if either operand is true.
So keeping those rules in mind - the first expression using && returns false and the second using || returns true. This is why the first rule keeps the the control enabled and the second does not based on you being user2.
Current User (Email)!='user1@s.com' (TRUE) && Current User (Email)!='user2@s.com'(FALSE) RETURNS false.
Current User (Email)!='user1@s.com' (TRUE) ||Current User (Email)!='user2@s.com' (FALSE) RETURNS true.
Thanks,
Mike