Just wanted to add my 8 month old world to this list also having this issue. I've been repeatedly attempting to open the world as suggested but this has not worked yet. First time this occurred we were about 15k blocks out from spawn looking for a woodland mansion (which ended up being around 22k blocks from spawn). I loaded an earlier backup and we were able to continue. however after returning to the spawn area this occurred again. Again having to return to an older copy and losing progress. Hope this is something Mojang will be addressing in the near future.
Hi, This issue is now resolved. I was able to log back in to my account today.