I have a 10 person realm that myself and a friend of mine have been playing on for about a year with no issues. I resonantly add a few people to the realm over several day with no issues. We started playing and added a new person and after about 30 mins of them playing with us the entire realm turned to a bedrock cube that everyone was trapped in. The dogs we had suffocated and the cube would change as we moved and the only way we could get out was to reset the realm back to a old save. the first time this happened was right after the new person broke a bee hive and we did see a command block in a mine cart. The realm turning to the bedrock happened a few times and the was one time that the entire inventory of on of the players emptied on its own.