I don't think deflation is an actual risk in this scenario ("value of that money plummets" = high inflation).
There are many stages between "people will starve" and having access to high quality food (and high QOL in general). For example if UBI is sufficiently high to allow most people currently employed in the food and service industries to not work (or to invest their time into gaining new skills etc.) I think a massive increase in food prices is unavoidable, at least in the short term until automation catches up. While basic foodstuffs would still remain affordable to all/most (the government would be forced to subsidize them if not), eating out and high quality, labor intensive products would likely become unaffordable to most people.
There are many stages between "people will starve" and having access to high quality food (and high QOL in general). For example if UBI is sufficiently high to allow most people currently employed in the food and service industries to not work (or to invest their time into gaining new skills etc.) I think a massive increase in food prices is unavoidable, at least in the short term until automation catches up. While basic foodstuffs would still remain affordable to all/most (the government would be forced to subsidize them if not), eating out and high quality, labor intensive products would likely become unaffordable to most people.