First, let's talk about utility. Utility of capital is non-linear. So, if we take $100 out of a millionaire's pocket, and distribute it evenly to 10 people who each have $100. The millionaire's ability to contribute to society has decreased by 10 units. The ten other members of society each had their ability to contribute to society increase by 2 units. We've generated a net-gain for society by redistributing wealth.
Second, we can look at the dollar value of the system. Yes, I would argue that even the dollar value of this redistribution is not a zero sum game. Obviously the basic transfer of wealth was zero sum. But it made our enonomy slightly more efficient by improving the capacity of the 10 citizens. Let's say the economy grows $10 more than it would have without the redistribution. Suddenly, even in just dollar-value the redistribution was not zero-sum.
It's important to realize that UBI is a response to extreme income inequality, which can cause large ineffeciencies in a market. Automation obsoleting jobs only needs to lead to UBI if that automation leads to rising income inequality. If we find a way to work with technology that keeps income disparities at a reasonable and efficient value, then there's no need for UBI. However, income inequality has reached to pretty significant heights and continues to grow.