I think you underestimate the amount of people that are content with not doing anything.
I'm more concerned with people who decide that they want to do something destructive. Staying up til 4am is possible when the food check comes no matter what. Deciding that you want to ruin someone's life by not letting them sleep ever seems like it could easily become a pastime.
[0]: https://www.businessinsider.com/chicago-considering-trial-fo...
Also concluded ones in Namibia and in India i think
I'm really not worried about the people who decide to do nothing (at least not in the first generation of UBI). I'm worried about the people who realize that now they can dress up as clowns and terrorize random people as a full time job because the food is coming regardless of what they do.
And Counting money is a bit harder than that. When I tip waitstaff, that income for them was my income before that and my employer's income before that and hospitals' income before that and, just maybe, that same waiter's income before that. But if instead it was medicare's money, it got an excellent ROI in terms of GDP output per tax dollar spent.