There is an issue I've been having when using nether portals, going in or out I'm stuck generating terrain. I'm playing on my realm and will be unable to use the nether, until this I fixed. It didn't happen for awhile and I've been able to go into the nether before with no issues, but this isn't the first time I've encountered it either. I also had this issue on my other worlds too, in single, or multiplayer.