I have an existing nether hub corresponding to roughly over world coordinates x:-6000, z:-6000. All of my portals were well linked to their over world/8 coordinates in the nether. Now, when I leave the nether it drops me in the neighborhood of x:150, z:-600. Moreover, no nether portal exists where I'm dropped, so I can't return to the nether. This seems to be a serious error in how the destination is calculated when generating terrain in an alternate dimension and needs urgent attention.