The economics suggest UBI is inflationary even if budgets are balanced. For several reasons -- the most 101 is that an increase in the real value of the welfare scheme decreases the labor supply, implying rising wages and therefore rising prices.
edit: consumption increases despite the distribution being balanced since it's assumed that the transfer is from a minority of tax payers with significant income/assets to a majority that sees a substantial increase to their minimum guaranteed cash flow.
Investment also reacts positively to the expectation of inflation, though that's getting more speculative. I think I've reached the limit of what I can do with Econ 101, but I hope to have shown that there's at least a principled claim to UBI being inflationary. Rising consumer price levels alone is inflationary under some definitions, and the effect on investment is not straightforward.