What happens to rents, for example? If everyone's income goes up, so does the rent. If everyone wanted to live in the same places, for the same reasons, and suddenly has higher incomes, they would bid up the rent, just as they do in well-paying urban areas. Would you be so comfortable if everyone used that free money and it established the bare minimum for living expenses?
And before you say it -- yes, I know, the core problem there is actually rent eating up everyone's discretionary income, their "slack" -- hence why I advocate dealing with that problem first (not just rent, but every such eater -- healthcare, education, etc) before letting those things leech the UBI too [2].
[1] yes, yes, up to the age/citizenship eligibility requirements, you get the point
[2] My earlier elucidation of this point: https://news.ycombinator.com/item?id=22604788