I had the same problem building in the Stonetalon Mountains a good bit ago!
... Maybe with the same Moonwell. Lol. Anyways, the problem here is that the client doesn't like the Moonwell. You'll find you can play the game as normal until you join the phase with the Moonwell, then it crashes. You may join the phase, but being anywhere near the Moonwell crashes you immediately. It also acts like this for another few other objects I believe.
(Sidenote: Yeah people can be a bit of an asshole and crash a phase either by spawning these objects or telling their victims to spawn them. I think it's bannable. Don't quote me, however!)
We'll have to be a good distance from the Moonwell so it doesn't crash you whilst also being close enough to check my solution worked. Which it should.
1 - Log into the character but don't join the phase
2 - Move to where the object will not load if you were to join the phase (For example I moved to the Barrens)
3 - Join the phase (If it still crashes, you're too close to the object- Move a bit further away!)
4 - Simply type .gob massdelete 20819
You can now join your phase without being bullied by the Moonwell.