UBI tests so far have found that most people working kept working, and the "indulging" was families being social, spouses becoming housewives/spouses, one parent at home with kids, ect. These aren't conclusive signs of long-term UBIs, of course.
I do actually anticipate rising costs alongside any UBI. Pretty much every job out there is an upwards cash vector, pretty much all your money goes back to the 1%, not your fellow John Does. Bills, car, mortage, insurance, services - how much goes to your neighbor? Anything taxed out will just promptly reconcentrate.
The UBI proles will have enough for gray, colorless uniforms, for corn and soy cubes, for living in terrafoam. The world already revolves heavily around the race to the bottom, and we're going to take the absolute bedrock and subsidize it. If you want even the slightest luxury, if you want to eat a piece of fruit that grew out of state, you'll need one of the few jobs left. Musician, poet, literal cock-sucker, one of the few slots we haven't automated. Yet. The equivalent of Prolekistan's trivial level of tourism, the rounding-error trickle of GDP that remains after their only export, labor, evaporates.
Unless you think we'll need billions of robot repairmen. Prolekistan should be fine, in that case. Otherwise, well, we all know what happens to countries with no exports.