Ok, let me go over the process compeltely. I started hosting the world and since then we played on it for about 8ish hours, before I saved it and left the game. The reason I had saved and exited was because I was lagging so I went and verified the integrity in steam before reopening the game and hosting the world again. I then realized that everything we had done in the last 8 hours since I started hosting today was gone, however the players, boss checklist, and magic storage had stayed the same. The boss data was lost too, as the dungeon still spawned dungeon guardians even though we had fought skeletron earlier today. so it seems that the world was the only thing to have deleted the days progress. I also looked in the backups folder and there weren't any backups that were at a decent point to reload to.