UPD2, 9:27 ET: Players will remain locked to parties until a new member joins or a new party is formed by the leader. We are working on a fix! In the meantime the party leader can kick the player from the party or players can also leave and reform the party.
UPD: The scheduled maintenance for Party Services has completed. Squad up and save the world!
We've begun scheduled maintenance on our Party Services. You may notice some limited functionality with those services during this time.
We'll provide a status update once this maintenance has completed.