There can be several reasons for this but don’t jump to the conclusion that the mink is “trap shy”. Mink tracks left during late winter-early spring and autumn may have been left by ‘transient’ animals moving through the area, either to find mates or to disperse. Sometimes they might have left the vicinity by the time you come to check your raft, the option here might be to shorten the raft checking interval to give a faster response time and set traps, not only on the raft where you found the tracks, but also on any adjacent ones.
If the tracks were large, it’s possible the animal entered your trap but did not trigger it. A very large male mink might stand on the front of the treadle plate with its nose up against the end mesh, and may not take the final step before turning around and leaving the trap. Most of the time we fine tune the cage traps we supply and moving the treadle forward one square is one thing we do to help increase the chance of a successful capture.
Try turning the trap around so the entrance is at the other end, it maybe that the mink prefers climbing onto the raft at one end. Keep an eye on what directions the tracks are going on the raft, they might all be going in one direction. This indicates that it may prefer going in that end and this is the way you should first set your trap.