I finally finished a build I've been putting off for months and was on day 3310. I got off the world and closed out Minecraft and got back on the next day. When I returned, I was in an older version of my world and the day was 3250, even though I saved at days 3300 and 3310. Luckily, I had a copy of my world saved at 3300, so I didn't lose too much progress, and for some reason, the world copy at day 3300 didn't roll back. I only ever experienced this on my Xbox even though I had 600 gigabytes left, and never experienced this on any other device, even though my other devices have way less than 600 gigabytes.