The best people, at least in industries where it fits, will move on to consult on the proper operation of the automation and others will become artisans doing highly crafted versions of what otherwise is mass-automated.
And some might move to other localities where the automation is too expensive to create or support. Automation has a cost relative to the market in which it's created and requires highly skilled people to create and maintain, whereas labor can be paid on a sliding scale based on their local cost of living and usually cost less than automation maintenance. That scales to low budgets better, especially if you don't produce quite so much of something as to hit the break-even point for automation.
UBI, in this context, is a mitigating strategy to keep the rest from becoming welfare recipients while they retrain or retire early. That would be a hell of a lot worse stigma than simply having a lower standing of living.
So while some people might have their standard of living brought up, many (possible many more than would be brought up) will be forced down with the inability to pull themselves back up because of lack of jobs.