It seems that the side effects of the traveller's backpacks aren't working. I tested this out with the lava cube (immune to fire damage) and the pumpkin ones (Endermen don't go aggro when stared at) but the special effects didn't seem to trigger

did you toggle the special effect on in the traveler backpack? they are off when you craft them and must be toggled on

Ah, that would do it. I didn't know you had to turn them on, thanks