There is already a post on this topic, where in total 3 people are stuck in the mining dimension as of writing this. I don't know much about crashes, but it seems that the crashes started happening a bit after I (ForriShizzle) loaded chunks around the natural mining dimension border at -30.000.000 X. When I first loaded chunks at the border there was a lot of lag, like it usually is at the border. I was able to play like normal in the mining dimension, but it's possible that the crashes started happening when a second person entered the dimension after the border chunks were loaded.
Also for some reason, when joining the server in the mining dimension, you are able to play for around 10-20 seconds before the server crashes. And yes, I have tried teleporting away, but it seems that there is extreme lag, making it impossible to teleport away.
