Remember also that a well-known limitation of economic measurements of GDP, productivity, etc. is that it doesn't account for personal work when no money changes hands. For example, a man who works full time and spends 100% of his salary on a nanny gets counted in GDP. But if he quits his job and takes care of the kid and the nanny takes his old job, then GDP and productivity have been reduced. Nothing has been changed about the amount of work done, but you've replaced two people working for money with only one working for money, so the accounting systems show it as less.

If part of the effect of minimum income is for people to spend more time with their kids, then this would show up as less work, in part, because less of the work being done would be for money.