The realm works perfectly up until I go exploring; when it crashes it really crashes and closes the whole realm for everybody for a good hour, then when we log back in it rolls back about 2 hours of work. The last rollback we had almost ended the server because we had just finished making a massive path around the map and digging a huge cave when it rolled back and undid it. 

I think it has something to do with loading new chunks because it only happens when somebody is exploring