The check is individual for each enemy, their trap detection vs your traps skill.
You can see your own trap detection skill in the stats overview.
Trap detection is determined by your perception, your level, equipment like motion detection goggles, feats like paranoia and your own traps skill. Enemies do just the same thing. You can also make it more difficult for enemies to spot your traps with the trap expert feat (+25% difficulty).
If enemies keep avoiding or disarming your traps, then your set trap skill is too low for the particular enemy.
Most often, this is because character level plays a big part in detection. On higher difficulties, you can encounter early on high level enemies (like lvl 10, 15, 20 etc) who have really high detection.
Edit: Animals dont care, they just run into your traps.
In your particular case, 38 traps skill is probably quite too low for the junkyard mutant area.
Equipping Trapper's belt, Jacknife, eating an eel sandwich to raise dexterity are all ways to increase your skill but you need more hard points if you want enemies to walk into traps consistently.
