[Trexmaster]

Debug: Trap level is 7. Success rate is 5. Roll was 1 (VS DC 70).
Debug: Trap level is 7. Success rate is 5. Roll was 3 (VS DC 70).
Debug: Trap level is 7. Success rate is 5. Roll was 3 (VS DC 70).
Debug: Trap level is 7. Success rate is 5. Roll was 2 (VS DC 70).
Debug: Trap level is 7. Success rate is 5. Roll was 2 (VS DC 70).
Debug: Trap level is 7. Success rate is 5. Roll was 5 (VS DC 70).

Multiple attempts on a chest in a 65 dungeon, disarm is maxed and I was using a grade 7 lockpick with both trap-related traits.

Same character on a chest from the Jammer Caves.

Debug: Trap level is 1. Success rate is 5. Roll was 5 (VS DC 10).
Debug: Trap level is 1. Success rate is 5. Roll was 1 (VS DC 10).
Debug: Trap level is 1. Success rate is 5. Roll was 3 (VS DC 10).

It seems like it's impossible to roll anything higher than 5, while the DC is 10 at the lowest. I tried another 30~ odd times but never got a roll higher than 5, so, I'm leaning toward that being the case.