I’m not sure of the exact steps to reproduce this, but I put three points into the Light Reading talent, and then equipped Master Thieves’ Armband replacing the tome. Then I tried to cast Sunray on an enemy and noticed it didn’t autotarget them. I had to do it manually. And now no ranged weapons or spells will auto-target enemies.

Quitting to the main menu or force closing the game didn’t help. The only thing that fixed auto-targeting was re-equipping the tome.

Anytime I equip Master Thieves’ Armband by replacing the tome, I lose autotargeting. However, if I manually unequip the tome first, I don’t lose autotargeting, not even when I equip the armband afterward.