I would wonder what limitations UBI would require. What if people get UBI in US and move to a low cost Asian or African country to live princely lives with their UBI while American taxpayers pay for that lifestyle.
Also, where would people move to? Many destinations are developing countries and thus the cost of living there will rise in the long term. Also, these expats would be heavily affected by foreign exchange rates.
People might indeed cluster up in certain places, buy property there and live a leisurely livestyle. These factors would make prices rise and in the long term it would become less attractive to move there. This happened in Spain where property prices in premium locations have skyrocketed because of well-off people from other EU countries buying homes there. Depending on how much the goverments of the target countries care about this, they might think about countermeasures, such as restricting property acquisition to locals.
If the outflux of money becomes significant, it will affect relations with the target country as the origin country will seek to reverse the flow. Trade deals will be affected, and developmental aids, if there are any, might be reduced. If it works, the target country might make it more difficult for expats to stay long-term. But the most straightforward approach might be to limit the UBI based on residency, or make the expat lose perks such as voting rights.