Hi all,
One story I have heard about mice taking the bait without setting the mouse trap off was by one mouse holding the
bait plate up with it's nose while it's conspirator takes the food from the trap.Seeing is believing though.

I had the same problem many years ago when the food would disappear without setting the trap off ,like
Gadge mentioned when the food is malleable it's removed without finding a dead mouse,as suggested
you can use a tougher bait but I would just use clear sticky tape to hold the bait on and I never had
the bait go missing again.

Cheers
Max.