So I have found that this has not only happened to me but other people as well. So what happened is I kicked all the people from my coop because they all stopped playing and hadent been on for a while but after I kicked them I was told by the people I live with to get off the computer so I logged off then the next day I got on and sold a diamond, next thing I know I do /home and I'v got a completely new island. Sorry I do not have the coordinates for my island but really hope someone could help!
So, there could be a number of reasons as to why this is happening to you, if you could give a more in depth description as to what happened to you we could pinpoint the reasoning behind this.
Well it was about 10 pm Australian eastern standard time that I kicked all of my coop members and then logged off. When I logged off I was still on the island. Then when I logged back on in the morning I was still on the island. I spent about 5 minutes on my island and then I was off to sell a diamond, witch I did leaving me 64 grass in my inventory. Then naturally I did /home to get to my island. But when I did that I was teleported to a completely new island. just like /warp skyblock (But without the cobblestone generator). So that's all that happened if you have any-more further questions or I just didn't articulate good enough, please let me know. Thank you. p.s after I kicked all the members it said something like that all the members where kicked and that the coop party is now over.