Villages, Ruined Portals, Ancient Cities, Woodland Mansions and Outposts will load in at the edge of render distance - then disappear as the player comes closer. 

Video attached of a village disappearing as I flew closer. 

We checked these structures and they did not disappear - Strongholds, Desert Temple, Jungle Temple, Ocean Monument, Mineshaft, Dungeons, Geodes, and Trial Chambers.