It does not usually break continuity, but it does not count toward the year either. The requirement is one continuous year of qualifying employment abroad within the preceding three years, and time worked in the United States for the same organization is normally excluded from the count while the three-year window is extended correspondingly.
Subtract the American months, then count again
Hypothetical example: Thibault has spent nineteen months as general manager of a Canadian residential-care group that is buying an American assisted-living operator. The mistake is to treat the qualifying year as elapsed time since appointment. It is a count of qualifying employment performed outside the United States.
Thibault's nineteen months as general manager include five during which he was working in the acquired properties, so the honest figure to present is fourteen months abroad, and the petition should present it that way rather than let a reviewer discover the gap. Two details decide whether even that figure holds. The employment abroad must itself have been managerial, executive or specialized-knowledge work; a year spent as an operations coordinator before promotion does not become qualifying because a later title does.
And the employer abroad must have been the same organization or a qualifying related entity throughout. Where a secondment was documented as an assignment by the Canadian company, continuity is easier to show than where the American entity issued him a local contract. Run this calculation against the regulation and current policy before drafting begins.