I have been playing Slime Rancher for a couple of days now and have beaten the game unlocking the end credits. (Day 100+) After hearing about the Vaults of treasure left behind I set out to find them. I found all 3 and opened 2 but when I arrived at the last vault door I realized I didn't have a Slime key to open it! (I've also opened every other gate/vault door in the game) Realizing that I didn't have a Slime key to the last available door for me to open I then spent the next 30min-1hr+ retracing my steps across the areas where I had already fed the Gordos that give you Slime keys. I even looked on the internet to see if there was anything I missed. In the end I went across ALL of the Gordo positions hoping to find a key that I may have missed, but to no avail. I'm not sure if I missed one of them and it despawned or something, but I am 100% positive I checked all Gordo locations and found nothing. So now I'm stuck with one last treasure room that I literally can't get into. Please help!
P.S.
Just wanted to say I love the game and look forward to future updates, keep up the good work :)