Way back in 1.2 in 2014 - when I was still a very new and inexperienced player - I got the Crimson Mold immediately after Hardmode began. To make space for my inventory, I put the item in my trash slot for some reason, then my game crashed. Character files do not save the item you have in you trash slot, so I lost the Crimson Mold.
More recently in 1.3 in 2019, while transiting from the surface to hell, I obtained a Rod of Discord. This was especially surprising because Hardmode had just began, and I was only attempting to casually mine. Usually it'd take me a few hours to get the Rod of Discord while actually farming for it.
Also during 2019, I got all 3 cellphone accessories from the Angler from the initial three quests. Sometimes, I'd get so unlucky, it would take many real-life days (sometimes weeks) just to get all 3 of them. On one occasion, I even got 10+ Sextants and 5+ Weather Radios but not a single Fisherman's Pocket Guide.