This is speculative but since the connections for mis-placed errors in hist-figs was implemented this bug was directly prior (without really knowing how Toady fixed the issue) maybe the dual/respawning hist figures attached to worldgen sites fail to remain consistent when they move off the map now, because the histfig system has been tightened to assign correctly leaving a lot of blank values in entities that assume hisfig.Meaning as soon as someone standing in place of a actual hist-fig drawn out of the 'invisible' people and population is made to move they lose their status because it reaffirms back to the genuine, that would need substantiating with duplicating companion bugs though. Actually someone at this note described a companion they took with them being duplicated but only being recognized as a single entity on companions screen but could physically see two carbon copies on inspection with 'l', the game recognised the companion unit limit though which could substantiate this.