I have minnow buckets, the floating kind that I’ve drilled holes in so they sit on the bottom.
They have strong spring loaded doors.
Anytime I leave sucker minnows and fatheads in them overnight they are gone, no trace.
What am I dealing with?

Turtles would be my guess buddy.

Human

Otter?

So we have this narrowed down to people, turtles or otter. No need to thank us.

Not saying it's aliens,...but it's aliens...

How deep are they? If they are less than 2 feet, I would guess racoon.

Is the lid open and is the trap still standing up on bottom???

Acid Rain.

Buckets are 4’ deep. My guess is turtles push open the door and most all of the minnows escape.

I agree, likely a big snapper. If it were to get "stuck" like a mink would with the lid closing, as soon as it retracts it's head into the shell it is free. Take a piece of snare cable, a big treble hook and a chunk of meat and see what is on it in the morning.