It's possible that floor 1 has trashcan mob for mutation room. Where it can be a problem is when your first and only room out of the starting room is a mutation room and 2 trashcans spawn. That's sometimes impossible for certain starters because you only have 10 tokens to spend at that point, and you can't avoid it to get extra token before the mutation room.
I'd suggest limiting trashcan mutation rooms on floor 1 to only 1 enemy, and more on floors 2 or 3.