Maldives holds an unbroken United Nations membership but left the Commonwealth and later rejoined
Background
The United Nations Member States page lists Maldives Date of Admission: 21-09-1965, so the country has been a UN Member State since 1965. The Commonwealth's own country profile for the Maldives records under Joined the Commonwealth: 1982; withdrew 13 October 2016, rejoined 1 February 2020. The Maldives therefore stood outside the Commonwealth for a little over three years, while its United Nations membership has run without a break. The profile also notes that the Maldives is a member of the Commonwealth Clean Ocean Alliance, the Blue Charter Action Group on tackling marine plastic pollution.
In plain words
Commonwealth of Nations — A voluntary association of states that a member may leave and later rejoin.