If we assume that income reflects society's demand for an individual's labor/skills/knowledge, and we arbitrarily increase income with no concomitant increase in demand then we have to assume something else is going to shift. A couple of outcomes seem likely to me:

* employer wages for low-demand workers will drop, as competition for low-demand workers will not increase, and those workers will accept a lower wage reasoning that the UBI 'makes up the difference'

* if employer wages are not allowed to drop below a certain point (the minimum wage), then more disposable income will create increased demand for scarce resources (e.g., housing that is a bit better than currently occupied) thereby causing prices to rise.

I'm no Econ major, so happy to hear how my reasoning may be in error.