I've been making a really elaborate world, in survival mode, set to peaceful only. From that I've got the 40.0 mb world save (if that helps any), and just started a portal (but built 3 in various locations), after making a couple hundred chickens, over a couple of weeks.
With this background info out of the way, I went into the Nether, with Oak fences, a gate and a pile of eggs. After spawning my own chicken farm in the Nether, every time I try to come back, it gets stuck on the loading screen, and freezes. After rebooting the game it leaves me at a portal, even after I disassembled it, so it shouldn't have even taken me to that spot. I've tried a few things like taking apart the extra portals, but it seems that the chicken farming in the Nether and/or the amount of saved stuff it needs to load when re-entering the normal map, locks everything up. I was able to come back before the chicken farming, with the only issue of missing visuals for certain parts of the map, if I went back and forth between realms, to fast. After the chickens, I have to reboot each time, when wanting to leave the Nether.