Upon entering a nether portal either in creative or in survival, cannot leave it in lieu of the fact the delay between loading worlds is so large it teleports you back to the opposite dimension in that time. For instance upon first entering a nether portal in the overworld you will get the 'downloading terrain' screen, then receive the getting deeper achievement, then be able to walk around in the nether briefly. However what's happened server side is you've been in the nether-side nether portal during the 'downloading terrain' screen and you will be updated back in the overworld side, but once it's done that you will again have teleported back to the nether during the time it's loading the overworld. In creative this continue endlessly as best I can tell, but in survival you take some damage, and you eventually die from suffocation damage. The server console reports lots of skipping ticks, and huge amounts of adding entity pending uuid duplicate errors. Because of this the nether is completely inaccessible. Note: no issues in singleplayer, as there's no delay like there is with the server.