I recently learned (after what you're describing happened to me and a Canvas quiz "randomly" (not quite!) disappeared when I copied another) that the second time you copy the same Canvas quiz, it overwrites the first copy (name/instructions/questions/settings), even if you had renamed/edited the first copy. That is how it is designed, surprisingly! This means that if you want to create multiple copies of the same quiz, you need to copy the latest copy each time and make sure that you never copy the same Canvas quiz more than once. For example, if you have a Canvas quiz named "Quiz 1", you can duplicate it by copying it into the same course, and then you will have two identical quizzes named "Quiz 1". If you copy the original quiz a second time (even after having renamed/edited the first copy), it will overwrite the first copy. In order to create more copies without overwriting the first copy, you can rename your first copy to, e.g., "Quiz 1 copy" so you can distinguish between the original and the first copy, and then in order to create one more copy of the same quiz, you copy the first copy, "Quiz 1 copy", instead of the original, and so on.